
Class T_A_55_i. 

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CHEMISTRY OF FOOD AND NUTRITION 



THE MACMILLAN COMPANY 

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TORONTO 



CHEMISTRY 



OF 



FOOD AND NUTRITION 



BY 

HENRY C. SHERMAN, Ph.D. 

PROFESSOR IN COLUMBIA UNIVERSITY 



SECOND EDITION 
REWRITTEN AND ENLARGED 



Ncto lark 

THE MACMILLAN COMPANY 
1918 

Ali rights reserved 






(\\'6 



Copyright, xgii and igiS, 
By the MACMILLAN COMPANY. 



Set up and electrotyped. Published February, 1911. 
Second Edition, Rewritten and Enlarged, March, 1918 



MAR 21 1918 

Nortoool! lPrfB8 

J. S. Cushinf? Co. — Berwick & Smith Co. 

Norwood, Mass., U.S.A. 

©CI.A494166 
..<h^.A 



PREFACE 

The purpose of this book is to present the principles of the 
chemistry of food and nutrition with special reference to the 
food requirements of man and the considerations which should 
underlie our judgment of the nutritive values of foods. Food 
is here considered chiefly in its relations to nutrition, the more 
detailed description of individual articles of food and the chemi- 
cal and legal control of the food industry having been treated 
in another volume. 

The present work is the outgrowth of several years' experience 
in teaching the subject and is published primarily to meet the 
needs of college classes. It is hoped that the book may also 
be of service to other readers who appreciate the importance of 
food and nutrition as factors in health and are interested in the 
scientific foundations which have been so greatly broadened 
and strengthened by the investigations of the past few years. 

While the small size, to which the book is limited by its main 
purpose, permits little of either historical or technically critical 
treatment, yet a limited number of original investigations and 
of controverted views have been discussed in order to give an 
idea of the nature of the evidence on which our present beliefs 
are based, and in some cases to put the reader on guard against 
theories which, while now outgrown, are still sometimes en- 
countered. 

Special attention has been given to the difficult task of at- 
tempting to present the striking results of some of the most 
recent investigations in nutrition in such a manner as to make 
clear their importance without giving exaggerated impressions 
and with due emphasis upon the fact- that on many significant 

V 



VI PREFACE 

points any interpretation which can now be offered is necessarily 
tentative. It is hoped that study of the text will be supple- 
mented by consultation of the references suggested at the close 
of each chapter, which should serve to put the reader in touch 
with much of the more significant literature and make him 
familiar with the scientific journals in which the future develop- 
ments of this rapidly growing subject may be followed as they 
appear. 

The author desires to express his indebtedness to the col- 
leagues and former students who have contributed many helpful 
suggestions and specifically to Doctors A. W. Thomas and M. S. 
Rose, Miss L. H. Gillett and Miss H. M. Pope for valuable 
criticism and assistance in the preparation of the present re- 
vision of the work. 

H. C. S. 

November, 1917. 



CONTENTS 



Introduction xi 

CHAPTER I 

Carbohydrates i 

Classification. Properties of the chief carbohydrates of food. 
References. 

CHAPTER II 

Fats axd Lipoids 19 

Fatty acids. Simple and mixed triglycerides. Formation and 
composition of natural fats. Storage of fat in the body. Fats and 
lipoids as body constituents. References. 

CHAPTER III 

Proteins 42 

Chemical nature and physical properties of proteins in general. 
Classification. Properties of some individual proteins. Relation 
between chemical constitution of the proteins and their food value. 
References. 

CHAPTER IV 

Enzymes and Digestion 69 

Classification and general properties of enzymes. Activity of 
the digestive enzymes. Salivary and gastric digestion. Intes- 
tinal digestion. Bacterial action in the digestive tract. Coeffi- 
cients of digestibility of food. References. 

CHAPTER V 

The Fate of the Foodstuffs in Metabolism .... 104 
Carbohydrate. Oxidation of carbohydrate. Production of fat 
from carbohydrate. Fat. Oxidation of fat. Storage of food fat 



viii CONTENTS 

PAGE 

in the body. Can carbyhodrate be formed from fat? Proteins. 
Absorption and distribution of protein digestion products. Utili- 
zation of protein in the tissues. I'ormation of carbohydrate from 
protein. Production of fat from protein. Fate of the nitrogen in 
protein metabohsm. References. 

CHAPTER VI 

The Fuel Value of Food and the Energy Requirement of the 

Body 138" 

Heats of combustion of the foodstuffs. The physiological fuel 
values of food materials. Table of loo-Calorie portions. Energy 
requirements in metabolism. Methods of study and amounts re- 
quired for maintenance at rest. References. 

CHAPTER VH 

Conditions Governing Energy Metabolism and Total Food Re- 
quirement 170 

Basal metabolism of the adult. Influence of muscular work. 
Influence of food. Regulation of body temperature. Influence 
of age and growth. References. 

CHAPTER VIII 

Factors Determining the Protein Requirement . . . 203 
Protein metabolism in fasting. Nitrogen balance experiments 
and the tendencj' toward equilibrium at different levels of protein 
intake. Protein sparing action of carbohydrates and fats. Pro- 
tein requirement in normal nutrition. Difference between mini- 
mum requirement and standard allowance of protein. Influence 
of the choice of food. Influence of muscular e.xercise. Protein 
requirement in relation to age and growth. References. 

CHAPTER IX 

Inorganic Foodstuffs and the Mineral Metabolism , . 234 
The elementary composition of the body. Metabolism of 
chlorides. Use of common salt. Metabolism of sulphur. ^Me- 



CONTENTS IX 



PAGE 



tabolism of phosphorus. Interrelations of phosphates, phospho- 
proteins, and phosphatids. Estimation of the phosphorus re- 
quirement. Phosphorus metabohsm with different amounts of 
phosphorus in the food. Phosphorus in food materials and 
typical dietaries. References. 

CIL\PTER X 

Inorganic Foodstuffs and the Mineral Metabolism (continued) 260 
Metabolism of sodium, potassium, calcium, magnesium. The 
calcium requirement. Calcium content of typical foods. Re- 
lations of the inorganic elements to each other. Inorganic ele- 
ments in American dietaries. Output of inorganic elements 
during fasting. The maintenance of neutrality in the body. 
References. 

CHAPTER XI 

Iron in Food and its Functions in Nutrition .... 285 
Development of modern views. The iron requirement of the 
body. Iron in foods. References. 

CHAPTER XII 

Antiscorbutic and Antineuritic Properties of Food . . 310 
Unidentified essentials in food. Scurvy and the antiscorbutic 
property of food. Infantile scurvy (Barlow's disease). Anti- 
neuritic properties of food. Attempts to isolate an antineuritic 
substance. Relation of chemical structure to antineuritic action. 
References. 

CHAPTER XIII 

Food in Relation to Growth and Development . . -331 
Nutritive requirements of the growing organism. Growth pro- 
moting substances in food. Influence of restricted food supply. 
Dietary deficiencies of individual articles of food. References. 

CHAPTER XIV 

Dietary Standards and the Economic Use of Food . . 360 

The general problem of a dietary standard. Energy allowances 
for adults. Energy allowances for children. The problem of a 



X CONTENTS 

PACE 

standard for protein. Opinions regardinp the value of liberal 
protein diet. Protein standards for children and for family 
dietaries. Standards for the calcium, phosphorus, and iron con- 
tent of the dietary. The unidentified essentials. The economic 
use of food. References. 

APPENDIX A 

Nomenclature and Classification of the Proteins . . . 403 

APPENDIX B 

Composition of Foods 407 

Explanation of tables. Edible organic nutrients and fuel values 
of foods. Ash constituents of foods in percentage of the edible 
portion. Protein, calcium, phosphorus, and iron in grams per 
100 Calories of food material. 



INTRODUCTION 

The activities on which the life of the body depends involve 
a continuous expenditure of energy and a constant exchange of 
material. Ultimately the body is dependent upon food for the 
fuel materials which supply energy and for both the substances 
which are transformed in, and eliminated from, the body, and 
those whose presence regulates and controls these transforma- 
tions. The materials leaving the body are to be regarded not 
merely as wastes but as end products of an orderly and co- 
ordinated series of chemical reactions which occur in the body 
and by virtue of which its functions are performed. Thus the 
chief functions of food are: (i) to yield energy, (2) to build 
tissue, (3) to regulate body processes. 

These functions involve reactions which are dependent upon 
the chemical composition and constitution of the food. Any 
food constituent which takes part in any of these functions may 
be regarded as having nutritive value. 

Most of the nutrient material contained in food requires 
more or less change to bring it into the exact forms most useful 
in nutrition. These changes as a rule take place in the digestive 
tract and together constitute the process of digestion. 

The changes which take place in the foodstuffs, after they 
have been absorbed from the digestive tract, are included under 
the general term "metabolism." Although the chemical' 
changes and the energy transformations are of course insepa- 
rable, it has become customary to speak of the metabolism of 
matter and the metabolism of energy, and to regard the extent 
of the metabolism of any material substance as measured by 
the amount of its end products eliminated, and the extent of 



xll INTRODUCTION 

the energy metabolism as measured by the amount of heat, or 
of heat and external muscular work, which the body gives ofif. 

The metabolism of matter and the metabolism of energy are 
normally supported by the food ; but if no food is taken, they 
continue at the expense of the body substance. The expendi- 
ture of energy can never cease in the living body because it in- 
cludes the work involved in carrying on the internal processes 
which are essential to Hfe itself ; and the expenditure of matter 
cannot cease because the energy for this necessary work is ob- 
tained by the breaking down of the organic compounds of the 
food or of the body substance into simpler compounds, many of 
which are of no further use to the body and must be eliminated. 
When the food suppUes sufficient energy, the body substance is 
protected ; when the food is insufficient, body substance is 
burned as fuel. In order, then, to consider intelligently the 
nutritive requirements of the body as regards the substances 
of which it is composed, it is necessary first to know whether 
the fuel requirements (the requirements of the energy metab- 
olism) have been fully met. 

The carbohydrates, fats, and proteins of the food all serve 
as fuel to yield the energy required for the activities of the body, 
and the proteins serve also as material for the maintenance or 
growth of body tissue. But of the fifteen chemical elements 
which are essential to the structure and functions of the body, 
simple proteins furnish only five. The remaining ten elements 
are largely constituents of the ash of the food and are known as 
ash constituents, inorganic foodstuffs, mineral matter, or salts. 

Recent investigations have developed the fact that food of 
sufficient energy value and containing ample amounts of each 
of the chemical elements known to be essential to the body is 
not necessarily adequate to meet all the requirements of nutri- 
tion. Thus it appears that certain substances occurring in 
natural foods but not yet chemically identified are also to be 
included among the nutritive requirements of the body and 



INTRODUCTION Xlll 

therefore among the factors which determine the nutritive 
values of foods. At present these unidentified substances are 
referred to as "vitamines" or as "fat soluble A" and "water 
soluble B." 

The essentials , of a chemically adequate food supply may 
therefore be summarized as follows : (i) sufficient of the organic 
nutrients in digestible forms to yield the needed energy ; (2) pro- 
tein, sufficient in amount and appropriate in kind ; (3) adequate 
amounts and proper proportions of the various ash constituents 
or inorganic foodstuffs ; (4) sufficient of each of the two un- 
identified "vitamine" factors, the "fat soluble A" and the 
"water soluble B." 

In attempting to give in the following pages a general view 
of the chemistry of food and nutrition it has seemed best to 
discuss first the chemical nature and nutritive functions of the 
substances which serve as sources of energy in nutrition, then 
the nutritive requirements in terms of energy, protein, the more 
prominent "inorganic" elements, and the "vitamines," and 
finally the bearing of these various factors of food value upon 
problems connected with the economic use of food. 



CHEMISTRY OF FOOD 
AND NUTRITION 



CHAPTER I 
CARBOHYDRATES 

Of the constituents of the ordinary mixed food of man the 
carbohydrates are usually the most abundant and the most 
economical sources of energy. They are also considered to be 
the first of the three great groups of foodstuffs to be formed by 
synthesis from simple inorganic substances in plants ; "in the 
long run, all the energy of Uving matter comes from them." 
The synthesis of carbohydrates in nature is therefore a logical 
starting point for the study of the organic foodstuffs. 

In the chlorophyll cells of the leaves of green plants the 
energy of the sun's rays brings about reaction between carbon 
dioxide and water which results in the hberation of oxygen and 
the formation of organic compounds. There is still doubt as 
to the exact mechanism of the process and no certainty that it 
is the same in all cases. It has, however, been quite generally 
found that the volume of oxygen hberated is equal to that of 
carbon dioxide consumed. The simplest possible representa- 
tion of the reaction would be 

CO2 + H2O ^ CH2O + O2 

according to which the first product of the synthesis would be 
formaldehyde. There is considerable (though not conclusive) 
evidence that formaldehyde is thus formed and that it is rapidly 
built up into less reactive compounds. Whatever the steps in 



2 CHEMISTRY OF FOOD AND NUTRITION 

the process* there is normally an early production of carbo- 
hydrate. Usually the first product which can be demonstrated 
as accumulating in the plant as the result of the photosynthesis 
is a sugar (glucose or sucrose) or starch. Assuming glucose as 
a typical product and neglecting the intermediate stages, the 
photosynthesis of carbohydrate may be represented thus : 
6 CO2 + 6 H2O -> CeHioOe + 6 O2 

Glucose is the most familiar representative of a group of simple 
sugars (monosaccharides or monosaccharoses) which are in 
composition direct polymers of formaldehyde (CH2O) and which 
are classified, according to the number of carbon atoms in the 
monosaccharide molecule, as trioses, pentoses, hexoses, etc. 

Classification 

Definitions of the term " simple sugar " vary somewhat, de- 
pending chiefly upon the views of different authors as to how 
simple a compound may properly be called a sugar. 

According to Browne, a simple sugar or monosaccharide may 
be defined as an aldehyde alcohol or ketone alcohol of the ali- 
phatic series, the molecule of which contains one carbonyl and 
one or more alcohol groups, one of the latter being always 
adjacent to the carbonyl group. All simple sugars contain, 
therefore, 

HC-OH 

I 

c=o 



* For concise discussion of the sj-nthesis of carbohydrates in plants the reader 
may be referred to Armstrong's The Simple Carbohydrates and the Glueosides, pages 
g2-g6; Browne's Handbook of Sugar Analysis, pages 532-534; and Mathews' 
Physiological Chemistry, pages 44-49. A somewhat fuller account will be found in 
Jost's Pflanzenphysiologie and Euler's P_flanzcnehcmif, and a very detailed treatment 
of the subject in Czapek's Biochemie der Pjlanzen. For discussion from a more 
physiological standpoint, see Pfeffer's Plant Physiology and summary of recent 
work by Jorgenson and Stiles in The New Phytologisl. 



CARBOHYDRATES 3 

as a characteristic group upon the presence of which the chief 
chemical properties of the sugars depend. 

The simplest possible sugar according to this definition is 
glycolaldehyde, CH2OH. — CHO, which (in analogy with the 
nomenclature of the familiar sugars) may also be called gly co- 
lose. The structural formulae of glucose and fructose, the most 
familiar representatives of the aldehyde-alcohol (aldose) and 
ketone-alcohol (ketose) sugars, respectively, are as follows : 



Glucose 


Fructose 


CH2OH 

1 


CH.2OH 


HOCH 


HOCH 


HOCH 


HOCH 


HCOH 

1 


HCOH 


HOCH 


C=0 


HC=0 


CHoOH 



Since glucose gives aldehyde reactions but not so readily 
as the above structural formula would lead one to expect, it is 
believed that in ordinary solutions of glucose the substance 
exists partly in the condition indicated by the aldehyde formula 
and partly in a tautomeric form represented by the lactone or 
" oxygen bridge " formula. 

Following are the aldehyde and lactone formulae written 
without reference to the spatial relationships of the hydrogen 
and hydroxyl groups : 

Aldehyde form : 

CHoOH— CHOH— CHOH— CHOH— CHOH— CHO 

Lactone form : 0— - 



CH.OH— CHOH— CH— CHOH— CHOH— CHOH 



4 CHEMISTRY OF FOOD AND NUTRITION 

The name monosaccharide (" single sugar ") implies that the 
monosaccharide molecule contains only one sugar radicle — that 
it cannot be spHt by hydrolysis into sugars of lower molecular 
weight. A substance Hke cane sugar which on hydrolysis spUts to 
two molecules of simple sugar is called a disaccharide or disaccha- 
rose (" double sugar ")• Trisaccharides and tetrasaccharides 
are also known. Substances which like starch are of high mo- 
lecular weight and on complete hydrolysis yield many molecules 
of simple sugar are called polysaccharides * or polysaccharoses. 
The term " carbohydrates " covers all the simple sugars and 
all substances which can be converted into simple sugars by hy- 
drolysis. The term " glucosides " is applied to substances which 
consist of combinations of carbohydrate radicles with radicles 
of other kinds and which therefore >'ield on hydrolysis both a 
simple sugar and one or more products of other than carbohy- 
drate nature. 

CLASSIFICATION OF CARBOHYDRATES f 

MONOSACCHARIDES (Monosaccharoses) 

Dioses (C2II4O2) — Glycolose. 

Trioses (CsHfiOs). 
Aldoses — Glycerose. 
Ketose — Dioxyacetone. 

Tetroses (C4H8O4). 

Aldoses — Erythrose,^ Threose.' 
Ketose — Erythrulose.- 

Pentoses (CsHjoOs). 

Aldoses — Arabinose,2 Xylose,^ Ribose,- Lyxose.' 
Ketoses — Araboketose^ Xyloketose (ketoxylose).* 
[Methyl pentoses (CeHioOj) — Rhamnose,- Fucose -]. 

* Some writers use the term polysaccharides to include all carbohydrates other 
than monosaccharides. Mathews applies it to all carbohydrates more complex than 
the disaccharides. 

t Names of a few of the most important carbohydrates are printed in small 
capitals. Separate mention of the d, I, and dl forms of the various sugars is omitted, 
since in the study of food and nutrition we are practically concerned only with that 
one of the three forms which is found in or derived from natural products. 



CARBOHYDRATES S 

Hexoses (C6H12O6). 

Aldoses — Glucose,! ^Mannose,^ Galactose,^ Gulose,'' Idose,' Talose,' 

Allose,' Altrose.' 
Ketoses — Fructose," Sorbose,^ Tagatose.^ 

Heptoses (CtHhO;). 

Aldose — Mannoheptose.i 
Ketose — Sedoheptose.^ 

Note. — No attempt is here made to summarize the occurrence of any but the 
tetroses, pentoses, hexoses and heptoses. Glycolose and the trioses if formed in 
nature are probably too reactive to accumulate sufficiently for identification. 

DISACCHARIDES (Disaccharoses). 
Dihexoses (Hexobioses) — (C12H22O11). 
A nhydride of glucose + fructose — Sucrose. 
Anhydrides of glucose + galactose — Lactose, Melibiose. 
Anhydrides of glucose -{- glucose — Maltose, Isomaltose, Trehalose, 
Turanose. 

TRISACCHARIDES (Trisaccharoses) . 

Trihexoses (C1SH32O16). 

Anhydride of glucose + galactose -{-fructose — Raffinose. 
Anhydride of glucose + glucose + glucose — Melezitose. 
A nhydride of fructose + fructose + fructose — Secalose. 

TETRA SACCHARIDES (Tetrasaccharoses) . 

Tetrahexoses (C24H42O21). 

Anhydrides of 2 galactose -(- glucose -\- fructose — Stachyose, Lupeose. 

POLYSACCHARIDES (Polysaccharoses) . 
Pentosans (chief constituents of gums and mucilages). 
Anhydrides of xylose — Xylans. 
Anhydrides of arabinose — Arabans. 

Hexosans. 

Anhydrides of glucose — Starch, Cellulose, Glycogen, Dextrin 

(and other "dextrans"). 
Anhydrides of mannose — Mannans. 
Anhydrides of galactose — Galactans (pectins). 
Anhydrides of fructose — Inulin (and other "levulans"). 

^Occurs free in nature. 

^ Not yet found free in nature (or only in small amounts) but obtained by hy- 
drolysis or fermentation of natural product. 

' Known only (with certainty) as a laboratory product. 



6 CHEMISTRY OF FCJOD AND NUTRITION 

PROPERTIES OF THE CHIEF CARBOHYDR.\TES OF FOOD 
Monosaccharides 

The monosaccharides are all soluble, crystallizable, diffusible 
substances, unaffected by digestive enzymes, and if not attacked 
by bacteria in the digestive tract, they are absorbed and enter the 
blood current unchanged. All of the three hexoses described 
below are susceptible to alcoholic fermentation, and are utilized 
for the production of glycogen in the animal body and the 
maintenance of the normal glucose content of the blood. A 
few of the leading facts regarding the occurrence in food and 
the nutritive relations of indixddual monosaccharides are given 
below. 

Glucose ((/.glucose, dextrose, grape sugar, starch sugar, 
diabetic sugar) is widely distributed in nature, occurring in 
the blood of all animals in small quantity (usually about o.i per 
cent) and more abundantly in fruits and plant juices, where it 
is usually associated with fructose and sucrose. It is especially 
abundant in grapes, of which it often constitutes 20 per cent 
or more of the weight of the fresh fruit and considerably more 
than half of the solid matter. Sweet corn, onions, and unripe 
potatoes are among the common vegetables containing con- 
siderable amounts of glucose. 

Glucose is also obtained from many other carbohydrates by 
hydrolysis either by acids or by enzymes, and thus becomes the 
principal form in which the carbohydrate of the food enters into 
the animal economy. In the healthy animal body the glucose 
of the blood is constantly being burned and replaced. In dia- 
betes the body loses to a greater or less degree the power to 
burn glucose, which then accumulates in excessive amount in 
the blood, from which it escapes through the kidneys. A tem- 
porary and usually unimportant loss of glucose in the urine 
may occur as the result of feeding large quantities at a time. 
This condition is known as alimentary glycosuria. Ordinarily 



CARBOHYDRATES 7 

any surplus of glucose absorbed from the digestive tract is con- 
verted into glycogen which, as described beyond, is readily 
reconvertible into glucose. Thus, while other carbohydrates 
occur in food in greater quantity, glucose occupies a very prom- 
inent place, partly because it is more widely distributed than 
any other carbohydrate, being a normal constituent of both 
plants and animals, and partly because it is the form in which 
most of the carbohydrate material of the food comes ultimately 
into the service of the body tissues (Chapter V). It is esti- 
mated that over half the energy manifested in the human body 
is derived from the oxidation of glucose. 

It is not to be inferred from the foregoing statement that 
the body obtains the energy of the glucose by oxidizing it di- 
rectly as such. The aldehydic properties of glucose make it 
susceptible to direct oxidation ; but, as the elaborate researches 
of Nef have shown, the glucose molecule in alkaline solution 
breaks up to form simpler substances of 2, 3, and 4 carbon 
atoms which are more readily oxidizable than glucose itself. 
There is strong evidence (Chapter V) that in the body tissues 
glucose is broken into 3-carbon molecules, which latter readily 
undergo oxidation. 

Fructose (J. fructose, fruit sugar, levulose) occurs with more 
or less glucose in plant juices, in fruits, and especially in honey, 
of which it constitutes about one half the sohd matter. It 
results in equal quantity with glucose from the hydrolysis of 
cane sugar and in smaller proportion from some other less 
common sugars. Fructose may occur in normal blood, but 
probably only in insignificant amounts. It serves, Hke glu- 
cose, for the production of glycogen ; and the fructose which 
enters the body either through being eaten as such or as the 
result of the digestion of cane sugar is mainly changed to gly- 
cogen on reaching the liver, so that it does not enter largely 
into the blood of the general circulation. Glucose and fructose 
are partially convertible, either one into the other, under the 



8 CHEMISTRY OF FOOD AND NUTRITION 

influence of very dilute alkalies. It is not surprising, there- 
fore, that fructose should be converted in the liver into glycogen, 
which on hydrolysis yields glucose. 

Galactose is not found free in nature, but results from the 
hydrolysis of milk sugar, either by acids or by digestive enzymes, 
and appears to have the same power as glucose and fructose to 
promote the formation of glycogen in the animal body. Anhy- 
drides of galactose, known as galactans, occur quite widely 
distributed in plants ; and galactosides, which are compounds 
containing galactose in chemical combination with radicles 
of other than carbohydrate nature, are found in the animal 
body, notably as constituents of the brain and nerve tissues. 

Disaccharides 

The three disaccharides here considered are di-hexoses or 
hexo-bioses of the formula C12H22O11, and are crystallizable 
and diffusible. Sucrose crystallizes anhydrous ; maltose and 
lactose, each with one molecule of water, which can be removed 
by drying at temperatures of 100° and 130° respectively. 
They are soluble in water; less soluble in alcohol. Lactose 
is much less soluble than sucrose and maltose. These disac- 
charides are important constituents of food and are changed to 
monosaccharides during the process of digestion. 

Sucrose (saccharose, cane sugar) is widely distributed in the 
vegetable kingdom, being found in considerable quantity, 
generally mixed with glucose and fructose, in the fruits and 
juices of many plants. The commercially important sources 
of sucrose are the sugar beet, the sugar and sorghum canes, the 
sugar palm, and the sugar maple ; but many of the common 
fruits and vegetables contain notable amounts. For example, 
sucrose is said to constitute at least half the solid matter of 
pineapples and of some roots such as carrots. 

On hydrolysis each molecule of sucrose yields one molecule 



CARBOHYDRATES 9 

each of glucose and fructose. These sugars all rotate the plane 
of vibration of polarized light, sucrose and glucose to the right 
( + ), and fructose to the left (-). The terms "dextrose" 
and " levulose," synonyms for glucose and fructose respectively, 
arose from this behavior of the sugars in rotating the plane of 
polarized light to the right and left. Since at ordinary tem- 
peratures the fructose rotates more strongly to the left than the 
glucose does to the right, the result of the hydrolysis of sucrose 
is to change the sign of rotation from + to — . For this reason 
the hydrolysis of cane sugar is often called " inversion," and 
the resulting mixture of equal parts glucose and fructose is 
known as " invert sugar." 

Sucrose is very easily hydrolyzed either by acid or by the 
sucrase (" invertase " or " inverting " enzyme) of yeast or of 
intestinal juice. So far as known neither the sahva nor the 
gastric juice contains any enzyme capable of hydrolyzing cane 
sugar, and the slight amount of hydrolysis which takes place 
in the stomach is beUeved to be due simply to the presence of 
hydrochloric acid. Under normal conditions the sucrose of 
the food passes mainly into the intestine unchanged and is 
there spHt by the sucrase of the intestinal juice, and the result- 
ing glucose and fructose are absorbed into the portal blood. 

When large amounts of sucrose are fed, some absorption takes 
place in the stomach; but the unchanged sucrose thus ab- 
sorbed appears to be largely, if not wholly, lost through the 
kidneys, as it is when injected directly into the blood current. 
Sugar eaten in concentrated form or in considerable quantities 
at a time is apt to cause irritation of the stomach either directly, 
or as the result of undergoing an acid fermentation, or in both 
of these ways. According to Herter sucrose and glucose are 
more likely to ferment in the stomach than is lactose. In cases 
where fermentation does not occur and the sucrose itself has no 
irritating effect, it may be especially useful as a rapidly avail- 
able foodstuff. However, it is not known that sucrose has any 



lO CHEMISTRY OF FOOD AND NUTRITION 

advantage over maltose and lactose in this respect, and the 
latter are less apt to irritate the stomach and cause indigestion. 

Lactose (milk sugar) occurs in the milk of all mammals, 
constituting usually from 6 to 7 per cent of the fresh secretion 
in human milk and 4.5 to 5 per cent in the milk of cows and 
goats. At the time of parturition, or if the milk is not with- 
drawn from the udder, some lactose may occur in the urine. If 
in such a case the mammary glands are removed, the percentage 
of glucose in the blood increases, and glucose (but no lactose) 
may appear in the urine (Abderhalden). These observations 
indicate that lactose is formed in the mammary gland and prob- 
ably from the glucose brought by the blood. 

Lactose is less sweet and much less soluble than sucrose, dis- 
solving only to the extent of about i part in 6 parts of water. 

When hydrolyzed either by heating with acids or by an 
enzyme, such as emulsin or the lactase of the intestinal juice, 
each molecule of lactose yields one molecule of glucose and 
one of galactose. In normal digestion, probably none of the 
lactose eaten is absorbed as such, for lactose injected into the 
blood is eliminated quickly and almost completely through the 
kidneys, whereas large amounts of lactose can be taken by the 
mouth without any such loss. As already noted, Herter found 
lactose to be less subject to fermentation in the stomach than is 
sucrose. Also, because of the much lower solubility, there is 
less danger of direct irritation of the stomach membrane by 
lactose than by sucrose. Recently Mathews has suggested that 
the occurrence in milk of lactose, a sugar having the galactose 
radicle, may be of special significance as a source of material 
for the synthesis of the galactosides of the brain and nerve 
tissues of the rapidly growing young mammal. 

Maltose (malt sugar) is formed from starch by the action 
of diastatic enzymes (amylases) and is therefore an important 
constituent of germinating cereals, malt, and malt products. 
It is also formed as an intermediate product when starch is 



CARBOHYDRATES II 

hydrolyzed by boiling with dilute mineral acids, as in the 
manufacture of commercial glucose. 

In animal digestion maltose is formed by the action of the 
ptyalin of the saliva or the amylopsin of the pancreatic juice 
upon starch or dextrin. The maltose-spHtting enzyme of the 
intestinal juice readily hydrolyzes maltose to glucose. Maltose 
is also readily and completely hydrolyzed by boiling with dilute 
mineral acids. In either case each molecule of maltose yields 
two molecules of glucose. 

While it is probable that little if any maltose is absorbed as 
such from the digestive tract under ordinary conditions, it is 
possible that such absorption may occur and that maltose as 
such may play a part in the normal carbohydrate metaboHsm ; 
for when injected into the blood it appears to be utilized to 
better advantage than either sucrose or lactose, and it may be 
obtained from glycogen by the action of diastatic enzymes in 
much the same way as from starch and dextrin. 

Polysaccharides 

The polysaccharides are all colloids insoluble in alcohol. 
Some " dissolve " in water in the sense that they form colloidal 
dispersions which will pass through filter paper ; some swell 
and become gelatinous ; some are unchanged. The members of 
greatest importance in nutrition are starch and glycogen, the 
typical reserve carbohydrates of plants and animals respectively. 

Pentosans, (C5H804)i, occur in the greatest variety of plants 
and in various parts of the plant organism. As a rule, how- 
ever, they are abundant only in the fibrous tissues and gummy 
exudations and not in the starchy and succulent parts which 
are more commonly used for human food. Moreover experi- 
ments have not yet succeeded in demonstrating in man or 
other mammals any enzyme capable of digesting the pentosans 
(Swartz). It is therefore believed that, notwithstanding their 



12 CHEMISTRY OF FOOD AND NUTRITION 

wide distribution in plants, the pentosans can play only a very 
small, if appreciable, part in the nutrition of man. 

Starch, (CeHioOs)!, is the form in which most plants store 
the greatest part of their carbohydrates, and is of great im- 
portance as a constituent of many food materials and as the 
source of dextrin, maltose, commercial glucose, and many fer- 
mentation products. Starch is found stored in the seeds, roots, 
tubers, bulbs, and sometimes in the stems and leaves of plants. 
It constitutes one half to three fourths of the solid matter 
of the ordinary cereal grains and at least three fourths of the 
solids of mature potatoes. 

Unripe apples and bananas contain much starch which is 
to a large extent changed into sugars as these fruits ripen, 
while, on the other hand, young tender corn (maize) kernels 
and peas contain sugar which is transformed into starch as these 
seeds mature. 

Unchanged starch occurs in distinct granules, and those 
formed in different plants vary in size and structure,* so that 
in most cases the source of a starch which has not been altered 
by heat, reagents, or ferments can be determined by microscopi- 
cal examination. Starch granules are scarcely affected by cold 
water ; on warming they absorb water and swell. Finally the 
starch passes into a condition of colloidal dispersion or semi- 
solution, " starch paste." Starch which has been heated in 
water (either admixed or naturally present with the starch as 
in a potato) until the granules are ruptured and the material 
more or less dispersed is very much more rapidly hydrolyzed by 
digestive ferments than is raw starch. 

To colloids such as starch, the usual methods of determining 
molecular weight are not applicable. It is certain, however, 
from the chemical complexity of some of the dextrins which 

* A very detailed study of the starch granules of different species of plants has 
been made by Reichert and published by the Carnegie Institution of Washington. 
(Sec references at end of chapter.) 



CARBOHYDRATES 1 3 

result from hydrolysis of starch, that the molecular weight of 
starch must be very high and its chemical constitution very 
complex. Probably the value of x in the formula (CeHioOs)! 
is very large, perhaps in the neighborhood of 200, corresponding 
to a molecular weight of about 32,000. For a full discussion of 
the more important facts bearing on the chemical constitution 
of starch, see the paper by Thomas cited in the list of refer- 
ences at the end of the chapter. 

Starch either in the soUd or in the " soluble " (dispersed) 
form is colored intensely blue when treated with iodine. This 
well-known reaction is deHcate and distinctive, but is now be- 
lieved to be due to colloidal adsorption rather than to the for- 
mation of a definite chemical compound. 

The term " starch," as we ordinarily use it, probably covers at 
least two substances. The more abundant of these, a-amylose 
(also called " amylopectin "), forms on heating in water a 
viscous opalescent paste, gives a somewhat purplish blue color 
with iodine, is evidently of great molecular complexity, and 
has recently been found to contain a small amount of phos- 
phorus * as an essential constituent. The less abundant com- 
ponent of starch, yS-amylose (also called " amylose "), forms 
when heated in water a clear, limpid solution which gives a 
pure blue color with iodine. The starch-digesting enzymes 
hydrolyze both a-amylose and )3-amylose, but not always with 
equal faciHty.f 

Starch on hydrolysis by means of acid gives first mixtures of 
dextrin and maltose, and finally glucose only as an end-product. 
The most satisfactory hydrolysis of starch to glucose is ac- 
complished by boiling or heating in a boiling water bath with 
hydrochloric acid of a concentration of about 2.5 per cent. 
When brought in contact with saliva, starch is hydrolyzed by 

* In the case of potato starch about 0.06 per cent. See papers by Northrup 
and Nelson and by Thomas referred to at the end of the chapter. 

t See paper by Sherman and Baker referred to at the end of the chapter. 



14 CHEMISTRY OF FOOD AND NUTRITION 

the ptyalin, with the formation of dextrin and maltose. A 
similar hydrolysis is affected by " amylopsin," the starch- 
splitting enzyme of the pancreatic juice, preferably known 
as pancreatic amylase (see terminology of enzymes, Chapter 
IV). 

" Soluble starch," largely used for laboratory experiments, is 
usually prepared by soaking raw starch in cold hydrochloric 
acid (about 7 per cent HCl) for several days, and then washing 
with cold water. 

Dextrins, (CeHioOs)^ or (CgHio05)x-H20, are formed from 
starch by the action of enzymes, acids, or heat. Small amounts 
of dextrin are found in normal, and larger amounts in germi- 
nating, cereals. Malt diastase, acting for some time upon starch 
in fairly concentrated solution, yields usually about one part 
of dextrin to four of maltose. During acid hydrolysis, dextrin 
is formed as an intermediate product between soluble starch 
and maltose. Commercial dextrin, the principal constituent 
of " British gum," is obtained by heating starch, either alone 
or with a small amount of dilute acid. 

The dextrins are much more soluble than the starches; and 
dextrin molecules while doubtless very large and complex are 
probably not over one fifth the size of starch molecules. 

The digestion of dextrin has already been mentioned in 
connection with that of starch, both saHva and pancreatic juice 
forming dextrin during the digestion of starch and acting upon 
it with the production of maltose. Complete hydrolysis of 
dextrin, as by boihng with acid, yields glucose as the sole 
product. 

Glycogen, (CcHioCOj;, plays much the same role in animals 
which starch plays in plants, and is sometimes called " animal 
starch." Glycogen also takes the place of starch as reserve 
carbohydrate in fungi and other forms of plant life not pro- 
\nded with the chlorophyll apparatus. It is a white, amor- 
phous powder, odorless and tasteless, which swells up and ap- 



CARBOHYDRATES 15 

parently dissolves in cold water to an opalescent colloidal dis- 
persion which is not cleared by repeated filtration, but loses its 
opalescence on addition of a very small amount of potassium 
hydroxide or acetic acid. Water solutions (dispersions) of 
glycogen are readily precipitated by alcohol. When treated 
with iodine they react yellow-brown, red-brown, or deep red. 
Hydrolysis of glycogen yields glucose only, as end-product. 

Glycogen occurs in the lower as well as the higher animals, 
and in all parts of the body, but is especially abundant in the 
liver. The amount of glycogen in the liver depends to a great 
extent upon the condition of nutrition of the animal. In the 
average of seven experiments by Schondorff in which dogs were 
fed for the production of as much glycogen as possible, 38 per 
cent of that found was in the liver, 44 per cent in the muscles, 
9 per cent in the bones, and the remaining 9 per cent in the 
other tissues of the body. But the distribution of glycogen in 
the body as shown by these experiments was quite variable, 
even among animals of the same species which had been fed 
in the same way. It is well known, too, that some species 
store glycogen in their muscles to a greater extent than others, 
attempts even having been made to distinguish analytically 
between horseflesh and beef by the difference in their glycogen 
content. The storage of glycogen in the body is promoted by 
rest as well as by Hberal feeding, and stored glycogen is used 
up rapidly during active muscular work. 

Cellulose, (CeHioOs)!, the chief constituent of wood and of 
the walls of plant cells generally, is an anhydride of glucose 
and can be made to yield the latter when hydrolyzed by suit- 
able treatment with strong acid. Typical cellulose of mature 
fiber (such as cotton, linen, or wood fiber) is, however, quite 
resistant to the action of dilute acids or of ordinary enzymes and 
passes through the digestive tract for the most part unchanged. 
The toughness of the cellulose differs with the stage of growth 
or maturity, and some of the less resistant forms of cellulose, 



1 6 CHEMISTRY OF FOOD AND NUTRITION 

such as that of tender whito. cabbage, may disappear from the 
digestive tract in appreciable amounts. Experiments to de- 
termine whether the cellulose thus disappearing is digested to 
sugar and absorbed or merely decomposed by bacteria in the 
digestive tract have not given conclusive results. According 
to Swartz : " In any event, the quantities of cellulose which the 
alimentary tract of man is capable of absorbing are, apparently, 
too small for it to play a role of any importance in the diet 
of a normal individual." The cellulose in the food may, how- 
ever, serve a very useful purpose in giving bulk to the food 
residues and thus facilitating their passage along the digestive 
tract. 

Hemicelluloses is a term somewhat loosely applied to poly- 
saccharides, usually occurring as constituents of cell walls in 
plants, which are not digested by the starch-spHtting enzymes 
but are usually much more readily hydrolyzed by acid than is 
cellulose. In many plant tissues the hemicellulose consists 
chiefly of pentosans ; in other cases it is largely mannan or ga- 
lactan. 

Mannans, (CeHioOs)!, anhydrides of mannose, are widely 
distributed in the vegetable kingdom and, as Swartz points out, 
show great differences in solubility, ranging from the readily 
soluble mucilaginous forms found in certain legumes to the 
horny matter of such seeds as the date, a form of mannan which 
was long confused with true cellulose. The experiments of 
Swartz upon the mannan of salep showed it to disappear com- 
pletely in its passage through the human digestive tract, al- 
though tests with individual digestive enzymes gave negative 
results. In what way and to what extent the mannan thus dis- 
appearing from the digestive tract becomes available in nu- 
trition is still a subject of investigation. 

Galactans, (CeHioOj)!, anhydrides of galactose, are widely 
distributed in plants. They occur in the seeds of legumes and 
to a slight extent in the cereals also, in by-products of beet 



CARBOHYDRATES 1 7 

sugar manufacture and abundantly in several of the algae and 
lichens, including Chinese moss, agar-agar, and Irish moss. 
The pectins are said to consist largely of galactans, apparently 
either in combination or admixture with pentosans and perhaps 
other complexes as well. The galactans differ in their solu- 
bihties and apparent digestibility when eaten by man or other 
animals, but on the whole do not appear to be of much nutri- 
tive value. Those of agar-agar and Irish moss, which are most 
used as food, are not digested. 

Levulans is the term under which a number of polysaccharides 
of the composition (CeHioOb)^, and yielding fructose (levulose) 
on hydrolysis have been described. The most important of 
these, at least so far as is at present known, is inulin, a white, 
powdery substance occurring in the tubers of the Jerusalem 
artichoke and to a less extent in the bulbs of onions and garlic 
as well as in various parts of plants not commonly used for 
food. By the action of acids inulin is very readily hydrolyzed 
to levulose, but the digestive juices do not seem to contain 
enzymes capable of hydrolyzing inulin and it appears to be of 
practically no importance as human food. 

REFERENCES 

Abderhalden. Physiologische Chemie (3. Aufl.). 
Abderhalden. Biochemisches Handlexicon. 
, Abderhalden. Handbuch der Biochemischen Arbeitsmethoden. 
Armstrong. The Simple Carbohydrates and the Glucosides. 
Armstrong. Article on Carbohydrates in Thorpe's Dictionary of Applied 

Chemistry (Revised Edition). 
Browne. Handbook of Sugar Analysis. 
Cohen. Organic Chemistry. 
CZ.A.PEK. Biochemie der Pflanzen. 
LippiiANN. Chemie der Zuckerarten. 
Mathews. Physiological Chemistry. 
Nef. (Behavior of the sugars toward alkalies and oxidizing agents.) 

Leibig's Annalen der Chemie, Vol. 357, page 214; Vol. 376, page i; 

Vol. 403, page 204. 
c 



l8 CHEMISTRY OF FOOD AND NUTRITION 

Northrop and Nelson. The Phosphorus Content of Starch. Journal 

of I he American Chcmkal Society, Vol. 38, page 472 (igi6). 
Reichert. The DilTerentiation and Specificity of the Starches in Relation 

to Genera and Species. Carnegie Institution of Washington, Publica- 
tion No. 173. 
ScHRYVER A.NTJ Hayxes. Pectin Substances of Plants. Biochemical 

Journal, Vol. 10, page 539 (1916). 
Sherman and Baker. Experiments upon Starch as Substrate for Enzyme 

Action. Journal of the American Chemical Society, \o\. 38, page 1885 

(1916). 
Svvartz. Nutrition Investigations on the Carbohydrates of Lichens, Algae 

and Related Substances. Transactions of the Connecticut Academy of 

Sciences, Vol. 16, pages 247-382 (1909). 
Thomas. The Phosphorus Content of Starch. Biochemical Bulletin, 

Vol. 3, page 403 (191 4). 
Thomas. The Chemical Constitution of Starch. Biochemical Bulletin, 

Vol. 4, page 379 (1915)- 
TOLLEN'S. Kurzes Handbuch der Kuhlcnhydrate. 



CHAPTER II 

FATS AND LIPOIDS 

Almost as widely distributed in nature as the carbohydrates, 
and constituting a much more concentrated form of fuel to 
supply energy in nutrition, are the fats. Fats are glyceryl 
esters of fatty acids, and since glycerol is a triatomic alcohol 
and the fatty acids are monatomic, a normal glyceride is a 
triglyceride and on hydrolysis yields three molecules of fatty 
acid and one molecule of glycerol. Thus, for example : 

C3H5(Cl8H3502)3 + 3 HoO ^ C3H5(OH)3 + 3 C18H36O2. 

Stearin Glycerol Stearic acid 

(glyceryl tristearate) 

When the splitting of the fat is brought about by means of an 
alkali instead of water, the corresponding products are glycerol 
and three molecules of the alkali salt of the fatty acid. Since 
alkali salts of the fatty acids are commonly known as soaps, 
this reaction is usually called saponification of the fat. 

The fats are therefore a definite group of chemical compounds, 
and the term appHes equally to the solid and the Hquid members 
of this group. As a matter of convenience, however, the 
liquid fats are often called " fatty oils." The fatty oils are 
also sometimes called " fixed oils," since a spot made by drop- 
ping a fatty oil on paper cannot be removed by drying (as can 
a volatile oil), nor by washing with water (as can glycerin). 

Another property which helps to characterize the fats is 
that glycerol, or the glyceryl radicle of a fat, when heated to a 
high temperature (300° C. or over), decomposes with production 
of acrolein, an aldehyde of characteristic odor and very irritating 
to the mucous membranes. Doubtless also fatty acid radicles 

19 



20 CHEMISTRY OF FOOD AND NUTRITION 

may sometimes conlributc to the production of irritating fumes 
when fat is overheated. 

The fats, including fatty oils, are lighter than water, their 
specific gravities ranging between 0.90 and 0.97. They are 
poor conductors of heat and therefore tend to conserve the 
heat of the body, while they show on oxidation a much higher 
fuel value than any of the other foodstuffs. 

All of the fats are practically insoluble in water, and all ex- 
cept those of the castor oil group are sparingly soluble in cold 
alcohol, but dissolve readily in petroleum ether and mix in all 
proportions with light petroleum oils. Light petroleum dis- 
tillate (" petroleum ether ") is often used as a solvent for fat. 
All of the fats are readily soluble in ether, carbon bisulphide, 
chloroform, carbon tetrachloride, and benzene. Since neither 
carbohydrates, proteins, nor ash constituents are soluble in 
ether (or the other " fat solvents "), it follows that the fat of a 
food may be readily separated from the other chief components 
by drying the food and extracting the dry material with pure 
ether. After the fat has been completely dissolved away from 
the other foodstuffs, it can be recovered from the solvent by 
evaporating the latter at a relatively low temperature. This 
is the method commonly used to estimate the percentages of 
fat in foods and to obtain small portions of fat for examination. 
It must be noted, however, that the fat thus obtained is not 
always pure in the sense of consisting entirely of substances 
meeting the definition of fat as given above. Obviously, such 
an extract will contain, along with the fat, any other ether-sol- 
uble substances which were present in the food, and may con- 
tain substances which, while not appreciably soluble in ether 
alone, are dissolved by the mixture of ether and fat. It is there- 
fore somewhat more accurate to speak of the material extracted 
by ether as " ether extract " rather than as " fat," and it will 
be found so designated in some statements of analytical results. 
In most human foods — at least those which are important as 



FATS AND LIPOIDS 21 

sources of fat — the constituents of the ether extract other 
than true fat are for the most part fat-Hke substances and we 
shall therefore be sufl5ciently accurate in most cases if we desig- 
nate the material extracted by ether by the simple term " fat," 
remembering, however, that we may thus include along with 
the glycerides (and any free fatty acids which may be present) 
small amounts oi fat-like substances or lipoids, and of fat-soluble 
or other ether-soluble matter. 

The food fats of commerce have been separated from the 
materials in which they naturally occurred not by solvents as 
above described but by mechanical means such as churning 
(butter) or pressing (olive or cottonseed oil) but even in this 
case the naturally occurring fat-soluble substances will still 
remain dissolved in the separated fat. Recent investigations 
indicate that these fat-like and fat-soluble substances, although 
occurring only in small quantities, may have very important 
functions in nutrition. We shall have occasion to study them 
in that connection later. 

The actual glycerides of any common natural fat, with the 
exception of butter, would if obtained absolutely pure be color- 
less, tasteless, and odorless. The colors, tastes, and odors of 
fats are therefore ordinarily due to substances present in small 
amount which might be removed by refining processes. All 
of the quantitative differences among the fats are to be accounted 
for by the kinds and the amounts of the fatty acids which enter 
into the composition of the glycerides. 

Fatty Acids 

The greater number of the fatty acids belong to a few homol- 
ogous series. The series to which stearic acid belongs may be 
represented by the general formula, CnHonOo, and is made up 
of homologues of acetic acid. The principal members of physi- 
ological importance are as follows: 



2 2 CHEMISTRY OF FOOD AND NUTRITION 

Acids of the Series C„H2„02 

Butyric acid (C^HsOi) occurs as glyceride to the extent of 
about 5 to 6 per cent in butter and in very small quantities in 
a few other fats. 

Caproic acid (C6H12O2) is obtained from goat and cow butter 
and coconut fat. 

Caprylic acid (C8H16O2) is obtained from coconut oil, butter, 
and human fat. 

Capric acid (C10H00O2) is obtained from coconut oil, butter, 
and the fat of the spice bush. 

Laurie acid (C12H24O2) occurs abundantly as glyceride in 
the fat of the seeds of the spice bush, and in smaller propor- 
tions in butter, coconut fat, palm oil, and some other vege- 
table oils. 

Myristic acid (C14H28O2) is obtained from nutmeg butter, 
coconut oil, butter, lard, and many other fats, as well as from 
spermaceti and wool wax. 

Palmitic acid (C16H32O2) occurs abundantly in a great va- 
riety of fats, both animal and vegetable, including many 
fatty oils, and also in several waxes, including spermaceti and 
beeswax. 

Stearic acid (C18H36O2) is found in most fats, occurring more 
abundantly in the soHd fats and especially in those ha\ang high 
melting points. 

Butyric acid is a mobile liquid, mixing in all proportions with 
water, alcohol, and ether, boihng without decomposition, and 
readily volatile with steam. With increasing molecular weight 
the acids of this series regularly show increasing boiling or 
melting points, decreasing solubiHty, and loss of volatihty with 
steam. For ordinary temperatures the dividing line between 
liquids and solids falls at about capric acid. Stearic acid is a 
crystalline soHd, insoluble in water, and only moderately soluble 
in alcohol and ether. 



FATS AND LIPOIDS 23 

Acids of the Series C„H2n-202 

These are unsaturated compounds. Each molecule contains 
one ethylene linkage or " double bond," and can take up by 
addition two atoms of halogen to form a saturated compound.* 
These unsaturated acids have, as a rule, much lower melting 
points than the saturated acids containing the same number 
of carbon atoms. The glycerides show correspondingly lower 
melting points than those of the saturated fatty acids and are 
therefore found more largely in the soft fats and the fatty oils. 
Such soft fats or fatty oils can be hardened to any desired con- 
sistency (up to that of stearin) by hydrogenation, which changes 
the unsaturated fatty acid radicles into the corresponding 
members of the saturated series. In recent years this process 
has been exploited commercially and large quantities of refined 
cottonseed oil are now hydrogenated to the consistency of lard 
and sold under trade names as lard substitutes. Other oils 
are also hardened by hydrogenation. 

Phycetoleic acid (Ci6H3o02) is obtained from seal oil and sperm 
oil ; an isomeric acid, hypogaic, occurs in peanut oil. 

Oleic acid (C18H34O2) occurs as glyceride in nearly all fats and 
fatty oils and is much the most important member of the 
series. Many of the typical oils of both animal and vegetable 
origin, such as lard oil and oHve oil, consist mainly of olein. 

Erucic acid (C22H42O2) is obtained from rape seed and mustard 
seed oils, and is not found in animal fats except when oils which 
contain this acid have been fed to the animal. 

The gradual change in physical properties with increasing 
molecular weight which is noticeable in the stearic acid series 
is not apparent in this series, probably because the known acids 

* The relative number of double bonds is measured analytically by determining 
the percentage of iodine which the fat or fatty acid will absorb. Thus pure oleic 
acid (mol. wt. 282) absorbs 2 atoms of iodine, giving an "iodine number" of go; 
pure Unoleic acid would absorb 4 atoms of iodine to the molecule, giving an "iodine 
number" about twice as great. 



24 CHEMISTRY OF FOOD AND NUTRITION 

of the series differ as regards the position of the double bond and 
are therefore not strictly homologous. 

Other Unsaturated Fatty Acids 

Acids of the series C„H2„_402, C„H2„-602, and CnH2„_802 
have been found to occur as glycerides in some of the fats. 
Linoleic acid, C18H32O2, and linolenic acid, C18H30O2, are the 
best known of these acids. They are found abundantly in 
linseed oil and in others of the so-called " drying oils," which on 
account of the affinity for oxygen of their highly unsaturated 
glycerides are gradually oxidized to solids on exposure to the 
air. Fatty acids having the same number of double bonds, but 
not the same property of oxidizing to hard, solid films are found 
in fatty oils of animal origin, especially those obtained from 
marine animals and from fishes. Since the acids of this series 
have still lower melting points than the corresponding acids 
of the oleic series, and since the physical properties of the glyc- 
erides follow those of the fatty acids which they contain, a fat 
containing an acid isomeric with linoleic or linolenic acid will 
be more fluid at any given temperature than one containing 
oleic acid in the same proportion. Hence, it is apparent that 
glycerides of the highly unsaturated and more fluid acids are 
physiologically adapted to the cold-blooded animals, and it is 
found that they are especially abundant in fish fat ; the acids 
of the series CnH2n_802 have been obtained as yet only from 
fish oils. 

" Simple " and " Mixed " Triglycerides 

Triglycerides in which the three fatty acid radicles are of the 
same kind are known as simple triglycerides. Tristearin, triolein, 
tripalmitin, etc., are examples of simple triglycerides. A mixed 
triglyceride is one in which the three fatty acid radicles are not 
all of the same kind. For example, distearo-olein (having two 
radicles of stearic and one of oleic acid), dioleo-palmitin (having 



FATS AND LIPOIDS 25 

two of oleic and one of palmitic), or stearo-oleo-palmitin (hav- 
ing one radicle each of stearic, oleic, and palmitic acids), is 
each a mixed triglyceride. 

It is evident from the chemical structure of glycerol that 
there can be only one simple triglyceride of any given fatty 
acid but that with two fatty acid radicles alike (Ro) and one dif- 
ferent (Ri) the triglyceride may have either of the following 
forms : 

H H 

I I 

HC-OR2 HC-ORi 

I I 

HC-ORi HC-OR2 

I I 

HC-OR2 HC-OR2 

I I 

H H 

That is, the two radicles of the same kind may be on the ter- 
minal carbons or may be adjacent. It will be noted that the two 
substances here represented have exactly the same compo- 
sition, but different constitution. 

If now the triglyceride contains one each of three different 
acid radicles (Ri, R2, R3) there are plainly three possible forms : 

H H H 



HC-ORi 

1 


HC-OR2 


HC-ORi 

1 


HC-OR2 

1 


HC-ORi 

1 


1 
HC-OR3 


1 
HC-OR3 

1 


HC-OR3 

1 


HC-OR2 

1 


1 
H 


1 
H 


1 
H 



Each of these three substances has exactly the same com- 
position, though the constitution is different for each. 



26 CHEMISTRY OF FOOD AND NUTRITION 

It should he noted that these five formula; represent types of 
structure and that the actual number of triglycerides possible 
from three fatty acid radicles is greater since we may have sub- 
stances corresponding to either of the first two in which R3 
replaces either Ri or R2 ; and it is plain that as the number of 
fatty acids is increased beyond three the number of possible 
mixed triglycerides increases very rapidly so that with the large 
number of fatty acids which are now known to be of fairly com- 
mon occurrence in fats the possible number of mixed triglycer- 
ides must be almost unlimited. The simple triglycerides cor- 
responding to the common fatty acids are all known, but 
naturally not all of the practically innumerable possible mixed 
triglycerides have been separated or prepared. 

Berthelot in 1869 suggested that fats probably contain 
mixed glycerides and in 1889 Blyth and Robertson reported a 
palmito-stearo-olein in butter, but it is only since Kreis and 
Hafner (1903) described the preparation of palmito-distearin 
from beef tallow and Bomer (1909) separated stearo-dipalmitin 
from mutton tallow and palmito-distearin from lard that the 
widespread occurrence of mixed glycerides in the familiar fats 
has been generally accepted. 

Among the other mixed glycerides reported as having been 
isolated from natural fats are : 

Myristo-pahnito-olein in cacao butter (Klimont, 1902), 
dipalmito-olein and stcaro-pahnito-ohin in tallow (Hansen, 1902), 
distearo-olein in cacao butter (Fritzweiler, 1903) and in Borneo 
tallow (Klimont, 1905), stearo-diolein in human fat (Partheil 
and Ferie, 1903). 

The fact long known to analysts that fats too nearly identical 
in composition to be distinguished by chemical analysis may still 
show differences in crystalline structure under the microscope 
is now explained as due to the presence of different mixed tri- 
glycerides containing the same fatty acid radicles. Thus beef 
fat rendered at such a temperature as to contain the glycer- 



FATS AND LIPOIDS 27 

ides of stearic, palmitic, and oleic acids in practically the 
same proportions as in lard still differs so constantly from lard 
in its microscopic appearance as to indicate the presence of dis- 
tinct chemical substances and has now been shown to contain 
different mixed triglycerides. 

The fact that tributyrin has an intensely bitter taste makes 
it seem probable that none of this substance occurs in butter 
but rather that the butyric acid in butter fat is in the form of 
mixed glycerides. Probably mixed glycerides are as abundant 
as simple glycerides in natural fats. 

Formation and Composition of Natural Fats 

Fats are formed both in plants and in animals. The con- 
ditions which determine fat formation, and the character of the 
fat formed in different species and under different conditions, 
are better known than the chemical steps involved in the 
process. It is hardly necessary to mention the fact that the 
true fats are composed of the same three chemical elements of 
which the carbohydrates are composed (carbon, hydrogen, 
and oxygen) and that since the fats contain less oxygen and 
more carbon and hydrogen than the carbohydrates, they con- 
stitute a more concentrated form of fuel or a more compact 
and hghter medium for the storage of energy for future use. 
The question therefore presents itself whether either the plant 
or the animal organism (or both) has the power to change car- 
bohydrate material into fat. 

Formation of Fat from Carbohydrate 

In plants there are many indications of the formation of fat 
from carbohydrate, as when decrease of starch and increase of 
fat go on simultaneously in a ripening seed, or when sugars are 
found to be constantly brought to a tissue in which fat is form- 
ing and there disappear as the formation of fat progresses. It 



28 CHEMISTRY OF FOOD AND NUTRITION 

is probably because no one has doubted the formation of fat 
from carbohydrate in plants that the process has not been more 
rigorously investigated. 

In animals it is certain that fat may be formed from carbo- 
hydrate. From the standpoint of our present knowledge it 
would seem that the readiness with which farm animals are 
fattened on essentially carbohydrate food should have been 
sufficient to convince early observers ; but this evidence appears 
to have been overlooked formerly because of the idea, for a 
long time prevalent, that simpler substances are built up into 
more complex compounds only in the plant, and not in the ani- 
mal organism. In recent years it has become necessary to aban- 
don this latter assumption completely, and there is now abun- 
dant evidence that the animal body synthesizes fat from 
carbohydrate. 

The most obvious method of demonstrating the conversion 
of carbohydrate into fat is that followed by Lawes and Gil- 
bert. Several pigs of the same Htter and of similar size were 
selected; some were killed and analyzed as " controls," while 
the others were fed on known rations and later weighed, killed, 
and analyzed to determine the kinds and amounts of material 
stored in the body. In several cases the amounts of fat stored 
during such feeding trials were found to have been much larger 
than could be accounted for by all of the fat and protein fed, so 
that at least a part, and in some cases the greater part, of the 
body fat must have been formed from the carbohydrate of the 
food. Many similar experiments have been made, and the 
transformation of carbohydrate into fat has been demonstrated 
by this method in carnivorous as well as herbivorous animals. 

It has also been shown that carbohydrates contribute to the 
production of milk fat. Jordan and Jenter kept a milch cow 
for fifty-nine days upon food from which nearly all of the fat 
had been extracted. During this period about twice as much 
milk fat was produced as could be accounted for by the total 



FATS AND LIPOIDS 29 

fat and protein of the food, and in addition the cow gained in 
weight and her appearance showed that she had more body fat 
at the end than at the beginning of the experiment. 

Instead of determining directly the fat formed in the animal 
fed on carbohydrate, the production of fat from carbohydrate 
may be demonstrated by keeping the animal experimented upon 
in a respiration chamber so arranged that the total carbon given 
off from the body may be determined and compared with the 
total carbon of the food. If in such a case the body is found 
to store more carbon than it could store as carbohydrate or pro- 
tein, it is safe to infer that at least the excess of stored carbon 
is held in the form of fat. Many such experiments upon dogs, 
geese, and swine have shown storage of carbon very much 
greater than could be accounted for on any other assumption 
than that a part of the carbon of the carbohydrates eaten re- 
mained in the body in the form of fat. 

Further evidence of the transformation of carbohydrate into 
fat in the animal body is obtained from the " respiratory 
quotient." The discussion of the quotient and the significance 
of the information which it furnishes, as also the study of the 
chemical steps through which the transformation of carbohydrate 
into fat may take place, will be taken up in connection with the 
general study of the fate of the foodstuffs in metabolism (Chap- 
ter V). 

Composition and Properties of Animal Fat 

Just as we found that the character of the fat of the cold- 
blooded animals is adapted to the maintenance of a fluid or 
plastic consistency at the low temperature to which it is ex- 
posed, so to a less degree the character of the fat of warm- 
blooded animals appears to vary with its position in the body 
and with the temperature to which the body is subjected during 
the time that the fat is in process of formation. Thus Hen- 
riques and Hansen concluded from experiments with pigs that 



30 



CHEMISTRY OF FOOD AND NUTRITION 



the thick layer of subcutaneous fat on the back, where it was 
not thoroughly warmed by the blood and therefore had an aver- 
age temperature considerably below that of the interior of the 
body, was richer in unsaturated compounds (olein, etc.) and 
had a lower melting point than the fat of the body as a whole ; 
while the fat from animals which had been grown in a warm 
room, or which had been heavily jacketed so that the skin was 
not exposed to cold air, contained near the skin fat of more 
nearly the same composition as in the interior of the body. 

Moulton and Trowbridge have observed that the fat in beef 
animals becomes richer in olein and therefore softer with age, 
with fatness, and with nearness to the surface of the body. 

Usually, however, the nature of the fat found in the body is 
more or less characteristic of each species or group of closely 
related species. Herbivora contain as a rule harder fats than 
carnivora, land animals have harder fats than marine animals, 
and all warm-blooded animals have fats which are decidedly 
harder than those found in fishes. The fats of different mam- 
mals were investigated by Schulze and Reineke, whose results * 
showed little variation from an average of carbon, 76.5 per cent ; 
hydrogen, 12 per cent; oxygen, 11.5 per cent, as may be seen 
from the following : 



Kind or Fat 


Carbon 


Hydrogen 


Oxygen 


Human fat f 

Beef fat 

Mutton fat 

Pork fat 


76.62 
76.50 
76.61 
76.54 


11.94 
II. 91 
12.03 
11.94 


11.44 

11-59 
11.36 
11.52 



The foregoing statements refer to the fat of the adipose tis- 
sues. In the fat extracted from the Hver, kidney, and heart, 

* Armsby's Principles of Animal Nutrition, page 6i. 

t Benedict and Osterberg {American Journal of Physiology, Vol. 4, page 6g) 
found in 8 samples of human fat an average of 76.08 per cent carbon and n.78 
per cent hydrogen. 



FATS AND LIPOIDS 3 1 

Hartley* finds fatty acids of the series C„H2„_402, C„H2„_602, 
and possibly C„H2„_802. 

A possible explanation of this difference between the fat of 
the adipose tissues and of the actively functioning organs is to 
be found in the greater reactivity of the unsaturated acid radi- 
cles. The saturated fatty acid radicles are relatively stable 
and inert ; and when the glycerides of such acids are deposited 
in the inactive adipose tissues, the fats may remain unaltered 
for a long time and accumulate in considerable quantities. 
The unsaturated fatty acid radicles are less stable and more 
readily acted upon and broken up. This is consistent with the 
fact that we find them more abundantly in fats of the organs 
in which metaboHsm is more active and has led to the view that 
the desaturation of fatty acid radicles by the active organs of 
the body may be an important preHminary to the metabolism 
of the fat. On the other hand, the formation of unsaturated 
fatty acid radicles such as oleic and linoleic does not, according 
to our present knowledge, seem essential to the " /8-oxidation 
theory " which is now generally held as most probably repre- 
senting the main course of fatty acid metaboHsm (Chapter V). 
It is therefore entirely possible that the highly unsaturated 
fatty acids found, for example, in the liver, may be present as 
constituents of the protoplasm of these cells, essential to the 
properties which enable them to carry out some of their func- 
tions but not necessarily connected with the metabolism of fat 
itself. 

Butter fat differs from body fat in containing fatty acids of 
lower molecular weight (particularly butyric acid, which is 
fairly characteristic of butter), and so shows a higher percent- 
age of oxygen and lower percentages of carbon and hydrogen. 
The most abundant acids of butter fat are, however, palmitic, 
oleic, and myristic, and the ultimate composition is not very 
greatly different from that of body fats. A sample of butter 

* Journal of Physiology, Vol. 36, page 17. 



32 CHEMISTRY OF FOOD AND NUTRITION 

fat analyzed by Browne* showed 75.17 per cent carbon, 11.72 
per cent hydrogen, and 13. 11 per cent oxygen. 

Storage of Food Fat in the Body 

In discussing the formation of body fat from carbohydrate it 
was shown that often the greater part of the fat stored is manu- 
factured in the body from carbohydrate. So striking were the 
results of some of the experiments demonstrating the synthesis 
of fat from carbohydrate, that physiologists came to question 
for a time whether any of the fat deposited in the tissues comes 
from the fat of the food. Abundant evidence that food fats 
may be directly deposited in the body has been obtained by 
feeding characteristic fats to dogs and showing that these fats 
can afterwards be recognized in the tissues of the animals. 
Experiments of this kind have been made, using Unseed oil, 
rapeseed oil, or mutton tallow, any of which is easily distinguish- 
able by its chemical and physical properties from the fat nor- 
mally found in the body of the dog. For example, Munk starved 
a dog for 19 days, and then for 14 days fed a mixture of the 
fatty acids obtained from mutton tallow, as a consequence of 
which about one half of the weight lost by fasting was regained. 
The dog was then killed and yielded on dissection iioo grams of 
fat melting at 40°, which is about the melting point of mutton 
tallow, whereas normal dog fat melts at about 20°. In another 
experiment by Munk rape oil was fed and the fat obtained from 
the dog was found to contain 82.4 per cent of oleic and erucic 
acids and 12.3 per cent of soHd acids, whereas normal dog fat 
had only 65.8 per cent oleic, no erucic, and 28.8 per cent of 
solid fatty acids. 

The occurrence in the body fat of properties usually char- 
acteristic of some particular fat which has been fed is now very 
well known and is recognized in estabUshing standards of purity 

* Journal oj the American Chemical Society, Vol. 21, page 823 (1899). 



FATS AND LIPOIDS 33 

for fats of animal origin. Thus, the lard obtained from swine 
which have been fed cottonseed meal shows the characteristic 
color reactions of cottonseed oil, and more elaborate tests 
must be made in order to determine whether cottonseed fat has 
actually been mixed with the lard. 

European food officials sought to establish an easy method 
of distinguishing between butter and its substitutes by requiring 
manufacturers of any butter substitute to use a certain pro- 
portion of sesame oil in the preparation, sesame oil having a 
characteristic color reaction which can be very easily demon- 
strated without the use of laboratory faciUties. It was found, 
however, that the same sesame oil reaction might be exhibited 
by a perfectly pure butter fat from cows which had been fed 
upon sesame meal. 

Evidence of the formation of body fat from food fat has also 
been obtained by experiments upon the total amount of fat 
formed in the body when the amount and composition of the 
food eaten was accurately known. Hoffmann starved a dog 
until its weight had decreased from 26 to 16 kilograms, so that 
it must have been almost devoid of fat. He then fed small 
amounts of meat and large amounts of fat for five days, after 
which the dog was killed and analyzed. The body contained 
1353 grams of fat, of which not over 131 grams could have 
come from proteins, and only a few grams at most from the 
small amount of carbohydrates in the meat fed, so that about 
nine tenths of the fat which the animal had laid on must have 
come from the fat of the food. 

Thus there is abundant experimental evidence that both 
the carbohydrate and the fat of the food may serve as sources 
of body fat. In a later chapter it will be shown that protein 
also may contribute to the production of fat in the body. 

A question naturally arises as to how, if proteins, fats, and 
carbohydrates of food may all contribute to the production of 
body fat, the nature of the fat can still be to any significant de- 

D 



34 CHEMISTRY OF FOOD AND NUTRITION 

gree characteristic of the species in which it is found. A partial 
explanation appears to be furnished by the recent work of 
Bloor, who finds that when the fat of the food has been spUt 
to glycerol and fatty acids in the course of digestion and these 
digestion products are taken up and resynthesized to fat in the 
intestinal wall, there may go into the resynthesized fat not only 
the fatty acid radicles of the food fat but also fatty acid radicles 
formed in the body. These latter, entering into the consti- 
tution of the absorbed fat, tend to give it some of the proper- 
ties characteristic of the species while at the same time some of 
the characteristics of the food fat may be retained. Thus when 
a dog is fattened by feeding mutton tallow which contains more 
stearin and less olein than ordinary dog fat the organism may, 
if the fattening is gradual, furnish enough oleic acid radicles to 
bring the resynthesized fat to the consistency ordinarily found 
in dog fat, or if the fattening is more rapid the oleic acid radicles 
may not be supplied at a sufficiently rapid rate to yield this 
result and the dog will then lay on fat of a character somewhere 
between that of mutton tallow and ordinary dog fat, the in- 
fluence of the food fat upon the character of the stored fat being 
more pronounced the more rapidly the fattening is carried out. 
It will be noted that, even if the fatty acid radicles synthesized 
in the body are built into the absorbed fat to such an extent as 
to bring its consistency and other physical properties to what is 
characteristic for the species, yet such body fat may still con- 
tain some radicles of fatty acids characteristic of the experi- 
mental food and not ordinarily found in the fat of the animal, 
as in the case of erucic acid in the experiment cited above 
(page 32). 

Fats and Lipoids as Body Constituents 

From what has been stated above, fat is seen to be a form 
of reserve fuel to which any of the organic foodstuffs may 
contribute (see also the discussion of fate of the foodstuffs in 



FATS AND LIPOIDS 35 

Chapter V). It is as reserve fuel that the large deposits of body 
fat are chiefly significant, but it should not be forgotten that 
even this " depot fat " may function as a protection to the body 
from mechanical injury and too rapid a loss of heat when exposed 
to cold, and as a packing and support to the visceral organs, 
particularly the kidneys. In recent years it has come to be rec- 
ognized that modified fats and fat-hke substances (Hpoids) are 
essential constituents of body tissues. Thus cell membranes are 
not simply walls of protein matter but probably are composed of 
both proteins and lipoids of different kinds and in varying pro- 
portions, and protoplasm is to be thought of as an emulsion of 
proteins and lipoids rather than as a jelly of proteins alone. 

Taylor, writing in 191 2, says: * " Fat plays two roles within 
the body. Fat represents the ultimate form of the storage of 
fuel, and the depot fats are quite the most inert and dead of 
any of the body structures. On the other hand, fats joined 
with protein and in complex combinations of still unknown 
composition, represent the most essential structures in cellular 
protoplasm, cell membranes, and in the central nervous system. 
The subjects of fat in its cellulometaboHc relations and fat in 
the energy metabolism are almost as distinct as though different 
substances were under consideration. Our information on the 
two subjects is not equal ; we know much concerning fat as 
fuel; we know little concerning fat in cellular structure." 

Mathews, in 1915,! writes: "It will be recalled that all 
living matter contains a larger or smaller amount of organic 
substances which are soluble in alcohol, ether, and other fat 
solvents. These substances help to give to protoplasm its 
properties of containing large amounts of water but not dis- 
solving ; and also the power of taking up readily and in large 
amounts chloroform, ether, and other substances soluble in fats 
but not readily soluble in water. They are among the funda- 
mental and ever-present constituents of living matter." 

* Digestion and Metabolism, page 342. f Physiological Chemistry, page 61. 



36 CHEMISTRY OF FOOD AND NUTRITION 

Following the suggestion of Gies,* Mathews includes all 
such substances under the group name of lipins (from the Greek, 
lipos, fat) which is thus made to cover both the true fats and 
all fat-like or lipoid substances. According to Mathews' classi- 
fication based on that proposed by Gies, the term " lipins " 
covers : " Alcohol-ether soluble constituents of protoplasm hav- 
ing a greasy feel and insoluble in water." These are divided 
into nine groups as follows : 

1. Fats and fatty acids, the term "fat" being here confined to those 
neutral glycerides which are solid at 20° C. 

2. Fatty oils (liquid at 20°C.) including (i) drying oils such as linseed 
oil, (2) semidrying oils such as cottonseed oil, (3) non-drying oils such as 
olive oil. 

3. Essential oils. Volatile, generally odoriferous, oil substances of varied 
chemical nature. 

4. Waxes. Esters of fatty acids with monatomic alcohols of high molec- 
ular weight such as the sterols. 

5. Sterols. Alcohols, generally of terpene group, soluble at ordinary 
temperatures. Cholesterol, phytosterol, etc. 

6. Phospholipins. Phosphatids. Fatty substances, yielding on hydroly- 
sis phosphoric acid and fatty acids (as well as glycerol). Lecithin, cephalin. 

7. GlycoHpins. Fatty substances free from phosphorus, yielding on 
hydrolysis fatty acids and a carbohydrate. Cerebron, phrenosin. 

8. Sulpholipins. Fatty substances, yielding on hydrolysis fatty acids 
and sulphuric acid. Sulphatide of brain. 

9. Aminolipins. Fatty substances, free from phosphorus, which contain 
amino nitrogen. 

Mathews remarks : " While the group of lipins contains such 
widely different chemical substances as the aromatic essential 
oils, like clove oil, the true neutral fats, like mutton tallow, the 
sterols, which are aromatic alcohols, and the phosphatids, or 
phospholipins, which contain large amounts of phosphoric 
acid, the members of the group all possess two or three proper- 
ties by virtue of which they are called lipins. These properties are 
their greasy or fat-Hke feel, their solubility in chloroform and fat 

* A more elaborate classification of the lipins is suggested by Gies and, Rosen- 
bloom in the article cited at the end of this chapter. 



FATS AND LIPOIDS 37 

solvents, and their insolubility in water. They constitute, then, 
a very heterogeneous group, chemically and physiologically." 

We have therefore, in the large heterogeneous group of sub- 
stances called lipins: (i) true fatty substances — fats, fatty 
oils, fatty acids, (2) fat-Hke or lipoid substances — some of these 
latter (Hke lecithin and other phospholipins) being closely 
related to the fats both chemically and biologically, others 
(like the sterols) showing little direct chemical relation to the 
fats but apparently bearing significant biological relationships, 
while still others (like certain of the essential oils) appear to 
bear httle relationship to the fats and to be classified as lipins 
merely because of their physical properties. If the term " Hpins " 
is to be so broadly used, it may be convenient to apply the 
term " lipoid " to substances other than fats or fatty acids but 
which are related to them chemically or biologically. 

Prominent among the lipoids (or fat-like substances other 
than true fats) are the sterols (solid alcohols) and the phospho- 
lipins or phosphatids. The latter are substances which contain 
a substituted phosphoric acid radicle in place of one or more of 
the fatty acid radicles of a fat. 

Sterols occur, at least in small amounts, in all natural fats. 
The best-known sterols are cholesterol (C27H44O) and phytosterol 
(C27H46O). Cholesterol occurs in animal fats, and phytosterol 
(or the closely related sitosterol) in those of vegetable origin. 
One method of determining whether vegetable fat is present in 
butter or lard is to examine for the presence of phytosterol, 
since phytosterol is not, like the substances to which the color 
reactions of cottonseed and sesame oils are due, carried over 
from the fat of the food to that of the animal body. 

Although its functions are not yet clearly defined, cholesterol 
appears to be a substance of much physiological significance. 
The name indicates " bile-solid-alcohol," as it was earhest and 
best known as a prominent constituent of gall stones. Its 
deposition in the form of gall stones is attributed to the presence 



38 CHEMISTRY OF FOOD AND NUTRITION 

of an insufficient amount of bile salts to keep the cholesterol of 
the bile in solution. It may also be deposited in the walls of 
the arteries. As a constituent of the blood cholesterol acts to 
protect the red blood cells against the action of hemolytic sub- 
stances, which unless neutrahzed by cholesterol would tend to 
cause anemia through excessive destruction of red corpuscles. 
According to Mathews, cholesterol is one of the most abundant 
lipins of the brain and occurs in nearly all Uving tissues; as a 
constituent of waxes and the sebum of the skin it protects the 
dermal structures ; it, or its degradation products, aids the other 
lipins in giving to cells their power of holding large quantities 
of water without dissolving or losing their peculiar semifluid 
characters ; it is believed to be the mother substance from 
which the bile acids are derived and so plays an important part 
in the intestinal digestion and absorption of fat ; and, on the 
other hand, cholesterol itself appears to check the action of fat- 
splitting enzymes in the body and thus to function as a regu- 
lator in the metabolism of the cell lipins. 

Phospholipins or phosphatids are also widely distributed in liv- 
ing cells and doubtless essential to their structure and functions. 

Of the phospholipins or phosphatids the best-known are the 
lecithins, which are abundant in egg yolk and occur also in 
significant quantities in brain and nerve tissue, blood, lymph, 
milk, many seeds, and other plant and animal tissues. The 
structure of lecithin has usually been represented by the formula 
H 

HC— OR 

HC— OR 

HC— O— PO(OH)— O— C2H4— N(CH3)0H. 

I 
H 

in which R stands for a fatty acid radicle. 



FATS AND LIPOIDS 39 

On hydrolysis such a compound would yield glycerol, fatty 
acids, phosphoric acid, and the nitrogenous base choline (tri- 
methyl oxyethyl ammonium hydroxide). If one of the radicles 
be that of oleic and the other that of palmitic acid the hydrolysis 
may be represented thus : 

C42H84NPO9 + 4 HoO^ C3H8O3 + C,8H3402 + C,6H3202 

Glycerol Oleic Palmitic 

acid acid 

+ H3PO4 + C5H15NO2 

Phosphor- Choline 

ic acid 

Recent investigations throw doubt upon the view that the 
nitrogen of typical lecithin is present only as choline groups. 

Taylor defines the simpler phosphatids as " lipoids in which 
two molecules of a higher fatty acid are combined with glycerol- 
phosphoric acid, to which is bound an amino body." 

A phosphatid which, like the above, contains one atom of 
nitrogen and one of phosphorus to the molecule is classified as 
a monamino-monophospholipin or monamino-monophosphatid. 
Monamino-diphospholipins, diamino-monophospholipins and 
triamino-monophospholipins have also been described. 

The fat of the active tissues of the body, as distinguished 
from that of the adipose tissue, seems to consist largely of 
phospholipins. Thus MacLean and Williams found 84 per cent 
of the total ether extract of pigs' liver to consist of phospholipins. 

Bang holds that it is " no mere coincidence that the most 
highly organized cells are always richest in lipoids." 

Other lipoids may also prove to be of much importance in 
nutrition. Butter fat and some other natural fats show nutri- 
tive functions which cannot be attributed to their glycerides 
alone and appear to be due to other substances soluble in fats 
and perhaps of the nature of lipoids. Such as yet unidentified 
fat-soluble substance appears to be absolutely essential to a 
fully complete diet since several investigators (Stepp, McCollum 
and Davis, Osborne and Mendel) have found it impossible to 



40 CHEMISTRY OF FOOD AND NUTRITION 

raise young animals to full maturity on rations apparently ade- 
quate otherwise but lacking in this " lipoid " of " fat-soluble " 
factor. These experiments will be cited more fully in con- 
nection with the discussion of the specific relations of food to 
growth (Chapter XIII). 

REFERENCES 

Abderhalden. Lehrbuch der Physiologischc Chemie. 

Abderhalden. Biochemisches Handlexicon. 

Abderhalden. Handbuch der Biochemischen Arbeitsmethoden. 

Bang. Chemie und Biochemie der Lipoide. 

Bloor. Absorption and Metabolism of Fat. Journal of Biological Chem- 
istry, Vol. II, page 429; Vol. 15, page 105; Vol. 16, page 517; Vol. 17, 
page 377; Vol. 19, page i; Vol. 22, page 133; Vol. 23, page 317; 
Vol. 24, pages 227, 447 (1912-16). 

Browne. The Chemistry of Butter Fat. Journal of the American Chemical 
Society, Vol. 21, pages 632, 823, 975 (1899). 

GiES AND Rosenbloom. Classification of the Lipins. Biochemical Bulletin, 
Vol. I, page 51 (1912). 

Glikin. Chemie der Fette, Lipoide und Wachsarten. 

Hammarsten. Textbook of Physiological Chemistry. 

Hartley. On the Fat of the Liver, Kidney and Heart. Journal of Physi- 
ology, Vol. 38, page 353 (1909)- 

Henriques and Hansen. Influence of Food Fat and Other Conditions 
upon Body Fat. Skandinavisches Archiv Physiologic, Vol. 11, page 151 
(1901). 

Jordan and Jenter. The Source of Milk Fat. New York Agricultural 
Experiment Station (Geneva, N. Y.). Bull. 132 (1897). 

Leathes. The Fats. 

Lewkowitsch. Oils, Fats and Waxes. 

MacLean and Williams. Nature of the Fat of the Tissues and Organs. 
Biochemical Journal, Vol. 4, page 455 (1909). 

McClendon. Formation of Fats from Proteins in Eggs of Fish and Am- 
phibians. Journal of Biological Chemistry, Vol. 21, page 269 (1915). 

Mathews. Physiological Chemistry. 

Mendel and Daniels. Behavior of Fat-Soluble Dyes and Stained Fat 
in the Animal Organism. Journal of Biological Chemistry, Vol. 13, 
page 71 (1913)- 

MouLTON and Trowbridge. Composition of the Fat of Beef Animals 



FATS AND LIPOIDS 4 1 

on Different Planes of Nutrition. Journal of Iiiduslrial and Engineering 

Chemistry, Vol. i, page 761 (1909). 
Richardson. Influence of Food and other Conditions on the Chemical 

Characteristics of Lard. Journal of the American Chemical Society, 

Vol. 26, page 372 (1904). 
Smedley. Formation of Fat from Carbohydrate. Biochemical Journal, 

Vol. 7, page 364 (1913). 
Taylor. Digestion and Metabolism. 
Ulzer and Klimont. Allgemeine und Physiologische Chemie der Fette. 



CHAPTER III 
PROTEINS 

Carbohydrates and fats are the chief sources of energy for 
the activities of the body, but not the chief constituents of which 
the active tissues are composed. Muscle tissue, for instance, 
is almost devoid of carbohydrate and often contains very little 
fat. The chief organic constituents of the muscles, and of the 
protoplasm of plant and animal cells generally, are substances 
which contain nitrogen and sulphur in addition to carbon, hy- 
drogen, and oxygen. Mulder, in 1838, described a nitrogenous 
material which he believed to be the fundamental constituent 
of tissue substances and gave it the name protein, derived from 
a Greek verb meaning " to take the first place." While Mul- 
der's chemical work did not prove to be of permanent value, the 
term which he introduced has been retained, and in the plural 
form, proteins, is now used as a group name to cover a large 
number of different but related nitrogenous organic compounds 
which are so prominent among the constituents of the tissues 
and of food that they may still be accorded some degree of pre- 
eminence in a study of the chemistry of food and nutrition. 

Proteins are essential constituents of both plant and animal 
cells. There is no known life without them. Plants build 
their own proteins from inorganic materials obtained from the 
soil and air. Animals form the proteins characteristic of their 
own tissues, but in general they cannot build them up from simple 
inorganic substances such as suffice for the plants, and must 
depend upon the digestion products obtained from the proteins 
of their food. Since animals must have proteins for the con- 
struction and repair or maintenance of their tissues, and since, 

42 



PROTEINS 43 

broadly speaking, they cannot make their proteins except from 
the cleavage products of other proteins, it follows that proteins 
are necessary ingredients of the food of all animals. 

Chemical Nature and Physical Properties of Proteins in General 

Generally speaking, the proteins of dififerent kinds of tissue, 
and even of the corresponding tissues of different species, are 
not identical substances. The total number of different proteins 
occurring in nature must therefore be very great. Of these, 
some fifty or sixty have been sufficiently isolated and studied 
to warrant description as chemical individuals. All of these 
have proven to be very complex substances and in no case has 
the chemical structure of a natural protein been fully deter- 
mined. It has, however, been shown that the typical proteins 
are essentially anhydrides of the following amino acids : 

AMINO ACIDS OF COMMON PROTEINS 

Monaminomonocarboxylic acids 

Glycine, amino-acetic acid, CH2(NH2) • COOH. 
Alanine, a-amino-propionic acid, CH3CH(NH2) ■ COOH. 
Valine, a-amino-isovaleric acid, (CH3)2CH • CH(NH2) • COOH. 
Leucine, a-amino-isocaproic acid (a-amino-isobutyl-acetic 
acid), 

(CH3)2CH • CH2 ■ CH(NH2) • COOH. 
Phenylalanine, phenyl-a-amino-propionic acid, 

C6H5CH2 • CH(NH2) • COOH. 
Tyrosine, oxyphenyl a-amino propionic acid, 

C6H4(OH) ■ CH2 • CH(NH2) ■ COOH. 
Serine, a-amino-)8-hydroxy-propionic acid, 

CH2(0H) : CH(NH2) • COOH. 
Cystine (dicysteine), or di-(a-amino-/8-thio-lactic acid), 

S-CH2-CH(NH2) • COOH. 

I 
S-CH2-CH(NH2) • COOH. 



44 CHEMISTRY OF FOOD AND NUTRITION 

Monaminodicarboxylic acids 

Aspartic acid, amino-succinic acid, 

COOH • CH2 • CH(NH2) • COOH. 

Glutamic (glutaminic) acid, amino-glutaric acid, 

COOH • CH2 • CH2 • CH(NH2) • COOH. 

Diaminomonocarboxylic acids 

Ornithine, a, 8, diamino-valeric acid, 

CH2(NH2) • CH2 ■ CH2 CH(NH2) COOH. 

Arginine, 8-guanidino-a-amino-valeric acid, 

NH 

(H2N)C- NH • CH2 • CH2 • CH2 • CH(NH2) • COOH. 

Lysine, a, c, diamino-n-caproic acid, 

CH2(NH2) • CH2 • CH2 • CH2 • CH(NH2) • COOH. 

Heterocyclic Amino Acids : 

Histidine, a-amino-/3-imidazol propionic acid, 

HC=C ■ CH2 • CH(NH2) • COOH. 

I I 
HN N 

CH 

Proline, pyrrolidin-carboxylic acid, 

H2C— CH2 

I I 
H2C CH • COOH 

\/ 
NH 



Trj^tophane, a-amino-/?-indol-propionic acid, 

HC^ "^C C • CH2 ■ CH • (NH2) • COOH. 

II 
CH 

/ 
QW ^NH 



HC^ yCv 



PROTEINS 



45 



It will be noted that these constituents of the protein molecule 
differ much in structure among themselves. They are, how- 
ever, alla-amino acids, i.e., the amino group (or one of them if 
there be more than one) is attached to the carbon atom adjacent 
to the carboxyl. 

In view of the wide occurrence of the alanine radicle in proteins and the 
frequency with which we shall have occasion to discuss the behavior of 
alanine (as a typical amino acid) in metabolism, it may be of interest to 
point out that several of the amino acids, even including some of unique 
constitution, may be regarded as derived from alanine by the substitution 
of a simple or complex radicle for one of the hydrogens on the /3 carbon of 
alanine. Thus by the substitution of an — OH or — SH group one obtains 
serine or cysteine respectively ; by substituting the phenyl or oxyphenyl 
group, there results phenylalanine or tyrosine ; by the imidazole (C3H3N2), 
histidine ; by the indol (CsHeN) radicle, tryptophane. 



CH3 



CH2OH 



CH2SH 



CHNH2 



CHNH2 



CHNH2 





COOH 




COOH 




COOH 




Alanine 




Serine 




Cysteine 


Cri2C6H6 




CH2C6H5OH 


CH2C3H3N2 


CHzCsHfiN 


CHNH2 

1 




CHNH2 

1 




CHNH2 

1 


CHNH2 

1 


COOH 




COOH 




COOH 


1 
COOH 


Phenylalanine 


TjTosine 




Histidine 


Tryptophane 



The Hnkage of the amino acid radicles in the protein molecule is 
chiefly through the carboxyl group of one amino acid reacting 
with the amino group of another. Thus two molecules of 
glycine combined by eHmination of one molecule of water 
yield glycyl-glycine, 

CH2NH2-CO 



CH2NH-COOH. 

which is the simplest of an immense group of anhydrides of 
amino acids, all of which are called " peptids." Dipeptids 



46 CHEMISTRY OF FOOD AND NUTRITION 

contain two amino acid radicles, tripeptids contain three, 
etc. Fischer, by uniting 7 to 19 amino-acid radicles, has pro- 
duced synthetic polypeptids which in some of their properties 
resemble the peptones, the simplest substances usually regarded 
as true proteins. Peptones are formed in nature by the diges- 
tive hydrolysis of ordinary proteins, whose structure is doubt- 
less considerably more complex. 

A certain analogy between carbohydrates and proteins may 
be noted. As starch on hydrolysis yields the polysaccharide 
dextrins, the disaccharide maltose, and finally as end product 
the monosaccharide glucose, so the native protein is hydrolyzed 
through peptones, polypeptids, and di- or tri-peptids, to amino 
acids. Thus the amino acid bears the same general relation to 
the protein which glucose bears to starch ; and just as the molec- 
ular weight of starch is very high and a single starch molecule 
yields a large (unknown) number of monosaccharide molecules, 
so the molecular weight of the protein is very high and the pro- 
tein molecule yields a large (unknown) number of amino acid 
molecules. There is, however, this important difference : the 
molecules of monosaccharide resulting from complete hydroly- 
sis of starch are all alike (glucose), whereas the complete hy- 
drolysis of any typical protein yields several of the above-men- 
tioned amino acids, in the case of most proteins from twelve to 
twenty. 

In view of the marked differences in structure existing among 
these amino acids it becomes important to know the relative 
proportions in which the various amino acid radicles exist in 
the different proteins. This is studied by hydrolyzing the pro- 
tein and separating and recovering as completely as possible the 
amino acids resulting from the hydrolysis. Since the recovery 
of the amino acids cannot be accomplished without loss, the 
results obtained are not strictly quantitative and our knowledge 
of the radicles which make up the protein molecule remains 
incomplete. It is believed by the investigators who have given 



PROTEINS 



47 



most attention to the question that the failure of the recovered 
amino acids to show a summation of one hundred per cent is 
more probably due to unavoidable losses in estimating the known 
amino acids than to the presence of other amino acids not yet 
identified. The accompanying table shows the percentages of 
amino acids obtained from four proteins occurring in different 
food materials. 

Percentages of AmNo Acids from Four Different Proteins * 





Casein 
(from Milk) 


Gelatin 


Gliadin 

(from 

Wheat) 


Zein 
(from Maize) 


Glj'cine 

Alanine 

Valine 

Leucine 

Proline 

Aspartic acid .... 
Glutamic acid .... 
Phem'lalanine .... 

Tyrosine 

Serine 

O.xyprolinc 

Histidine 

Arginine 

Lysine 

Tryptophane .... 

Cystine 

Ammonia 


o.oo 
1.50 

7.20 

9-35 
6.70 

■1-39 

15-55 

3.20 

4-50 

•50 

•23 

2.50 

3.81 

7.61 

1-5 
.06 
1.61 


16.5 

0.6 

I. 

9.2 
10.4 

1.2 
16.8 

I. 

0. 
•4 

3.0 
•4 

9-3 

6. 

0.0 

•4 


0.00 
2.00 

3-34 
6.62 

13.22 
0.58 

43.66 

2.35 
1.50 

•13 

1.84 
3-i6 
0.92 

I.O 

•45 

5.22 


0.00 

13-39 
1.88 

19-55 
9.04 

1. 71 
26.17 

6.55 
3-55 
1.02 

.82 

1-55 
0.00 
0.00 

3-64 


Summation 


67.21 


76.21 


85.67 


88.87 



From the data given in the table it will be seen that the pro- 
portions in which a given amino acid radicle occurs in various 

* In general each figure given in the table is the highest of the results reported 
In recent investigations. This is deemed more accurate than to give average results, 
because of the unavoidable losses referred to above. 

The data given for casein, gliadin, and zein are taken chiefly from the work of 
Osborne and his associates; those for gelatin chiefly from that of Skraup and 
Behler. 



48 CHEMISTRY OF FOOD AND NUTRITION 

proteins may be quite different. The four proteins here shown 
yield from o.o to 16.5 per cent of glycine; from 0.6 to 9.8 per 
cent of alanine; from i.o to 7.2 per cent of valine, from 6.6 to 
19.6 per cent of leucine. Of lysine, zein yields none, gliadin about 
I per cent, gelatin 6 per cent, and casein about 8 per cent. Of 
tryptophane, zein and gelatin yield none, gliadin about i per 
cent, casein about 1.5 per cent. 

For more detailed comparisons of the percentages of amino 
acids in different proteins and also in the flesh of four widely 
separated species, the more extended table further on in this 
chapter may be consulted. Whether it be essential that the 
proteins of the food shall furnish all the amino acids which the 
body proteins contain will naturally depend upon whether the 
body is able to make individual amino acids or not. Experi- 
mental evidence has shown that the animal body can make 
glycine readily, so that the absence of glycine radicles in the food 
proteins does not detract from their nutritive value. On the 
other hand the animal body does not seem able to make tryp- 
tophane, and as this is an essential constituent of body tissue 
the food proiein must always furnish tryptophane if it is to meet 
the needs of animal nutrition. Feeding experiments have also 
shown that the rate of growth of young animals may be largely 
influenced by the lysine content of the proteins fed ; food pro- 
teins in which lysine is lacking or inadequate may suffice for the 
maintenance of full grown animals but fail to support normal 
growth in the young of the same species. 

Such facts as these make it important that we study the 
proteins not only as a group but also individually and that we 
learn as much as possible about the kinds and amounts of 
amino acid radicles in the individual proteins. 

The ultimate composition of the proteins shows a general 
similarity throughout the group. All contain carbon, hydro- 
gen, oxygen, nitrogen, and sulphur; some also phosphorus 
or iron. 



PROTEINS 



49 



Composition of Some Typical Proteins according to Osborne 





Carbon 


Hydro- 
gen 


Nttro- 

GEN 


Oxygen 


Sulphur 


Iron 


Phos- 
phorus 




CENT 


PER 
CENT 


PER 
CENT 


PER CENT 


PER CENT 


CENT 


PER 
CENT 


Egg-albumin 


52.75 


7.10 


15.51 


23.024 


1.616 






Lact-albumin . 


52.19 


7.18 


15.77 


23.13 


1-73 






Leucosin . . . 


53-02 


6.84 


16.80 


22.06 


1.28 






Serum-globulin 


52.71 


7.01 


15.85 


23.32 


I. II 






Myosin . . . 


52.82 


7. II 


16.67 


22.03 


1.27 






Edestin . 




51.50 


7.02 


18.69 


21.91 


0.88 






Legumin . 




51.72 


6.95 


18.04 


22.905 


0.385 






Casein 




53.13 


7.06 


15.78 


22.37 


0.80 


— 


0.86 


Ovo-vitellin 




51.56 


7.12 


16.23 


23.242 


1.028 


— 


0.82 


Gliadin . 




52.72 


6.86 


17.66 


21.733 


1.027 






Zein . . 




55.23 


7.26 


16.13 


20.78 


0.60 






Oxyhemoglobin 


54.64 


7.09 


17.38 


20.165 


0.39 


0.335 






It will be seen that all these typical proteins contain 51 to 
55 per cent carbon, about 7 per cent hydrogen, 20 to 23 per cent 
oxygen, 15.5 to 18.7 per cent nitrogen, 0.3 to 2.0 per cent sulphur. 
Other typical proteins thus far studied have shown ultimate 
composition within these same limits. 

Similarity of elementary composition is entirely consistent with the 
belief that there may be an enormous number of chemical individuals among 
the proteins of nature. 

Fischer has recently illustrated the vast number of isomers which may 
exist among polj^jeptids and proteins by pointing out that a synthetic 
19-peptid obtained by linking 15 glycine and 4 leucine molecules is only 
one of 3876 possible isomers, without considering the tautomerism of the pep- 
tid linking. When more than two kinds of amino acids are involved, the 
possible number of isomers increases very rapidly. If a protein be imagined 
made up of 30 molecules of 18 different amino acids, one taken twice, one 
3 times, another 3, one 4, one 5 times, and 13 taken once each, there would 
be 10-^ isomers even if there were no tautomerism of the peptid group and 
if the linking took place only in the simple way as with monamino-mono- 
carboxylic acids. 

It is easy to see that when one considers not only isomerism but the vast 
number of compounds of slightly different composition which can be obtained 
E 



50 CHEMISTRY OF FOOD AND NUTRITION 

by varying the kinds and proportions of the amino acid radicals in the 
protein molecule, the possible number of different proteins of very similar 
elementary composition is practically unlimited. 

Probable molecular weights. — From the results of ultimate 
analysis an appro.ximate indication of the minimum molecular 
weight may often be obtained by a very simple calculation. 
Thus, oxyhemoglobin contains only 0.335 per cent of iron, and 
since there must be at least one iron atom in the molecule, it is 
obvious from a simple proportion making use of the atomic 
weight of iron, 

0.335 : 56 : : 100 : x, 

that the molecular weight of hemoglobin must be in the neigh- 
borhood of 16,800 or a multiple of this. 

To take an example from the simple proteins, zein contains 
0.60 per cent of sulphur, of which one third is much more readily 
spHt off than the other two thirds, from which it appears that 
the molecule contains three, or a multiple of three, sulphur 
atoms. Then by the proportion, 

0.60: (32 X 3) :: 100: X, 

it is found that about 16,000 or a multiple thereof is the probable 
molecular weight of zein. 

Estimates of the same order of magnitude are obtained if we 
base our calculations on the proximate rather than the ulti- 
mate analyses of the purified protein preparations. Osborne, 
Van Slyke, Leavenworth, and Vinograd have recently concluded 
from a very searching investigation that the lysine content of 
gliadin must lie between 0.64 and 1.20 per cent. Since the 
molecular weight of lysine is 146 it follows that the correspond- 
ing minimum estimate of the molecular weight of ghadin must 
fall between 12,000 and 23,000. The experimental facts do 
not permit the assumption of any lower molecular weight but 
are not inconsistent with the view that the true molecular weight 
may be some multiple of this. 



PROTEINS 51 

Physical properties. — In only a few cases have proteins 
been obtained in crystalHne form. Generally speaking the 
proteins may be regarded as typically colloidal substances. This 
does not preclude the beUef that in the tissues and fluids of the 
body the proteins may exist largely in combination with elec- 
trolytes. In view of the fact that the behavior of proteins in 
the tissues is largely dependent upon their colloidal character 
it is of interest to bear in mind the very high molecular weights 
of the proteins as mentioned in the last paragraph. Discus- 
sions of colloids commonly emphasize the fact that the smallest 
particles demonstrable under the ultramicroscope must still 
be of quite a different order of magnitude from that calculated 
for ordinary molecules. In such a case as that of starch or a 
typical protein, however, the probable molecular weight is so 
enormous as to make it a debatable question whether the in- 
dividual molecules may not constitute colloidal particles when 
dispersed in water (Bayliss). 

The proteins are insoluble in all of the solvents for fats 
(ether, acetone, chloroform, carbon disulphid, carbon tetrachlo- 
rid, benzene, and petroleum distillate). They differ in their 
solubilities in water, salt solutions, and alcohol, and these dif- 
ferences play a considerable part in the present schemes of 
classification. 

Classification. — There was formerly considerable confusion 
in the classification and terminology of the proteins and some 
differences of usage will still be met in the literature. At pres- 
ent, however, the majority of writers follow the recommenda- 
tions made by a joint committee of the American Physiological 
Society and the American Society of Biological Chemists in 
December, 1907. The full text of these recommendations will 
be found in the appendix. The following is an outUne of the 
classification thus recommended ; to which have been added 
examples covering most of the food proteins thus far described 
as chemical individuals. 



52 CHEMISTRY OF FOOD AND NUTRITION 

I. Simple Proteins. Protein substances which yield only 
amino acids or their derivatives on hydrolysis, 

(a) Albumins. Simpleproteinssolubleinpurewater andcoag- 
ulable by heat. Examples: egg albumin, lactalbumin (milk), 
serum albumin (blood), leucosin (wheat), legumelin (peas). 

(b) Globulins. Simple proteins insoluble in pure water, but 
soluble in neutral salt solutions. Examples: muscle globulin, 
serum globulin (blood), edestin (wheat, hemp seed, and other 
seeds), phaseolin (beans), legumin (beans and peas), vignin 
(cow peas), tuberin (potato), amandin (almonds), excelsin 
(Brazil nuts), arachin and conarachin (peanuts). 

(c) Glutelins. Simple proteins insoluble in all neutral solvents, 
but readily soluble in very dilute acids and alkaHes. The best- 
known and most important member of this group is the glu- 
tenin of wheat. 

{d) Alcohol soluble proteins. Simple proteins soluble in 
relatively strong alcohol (70-80 per cent) but insoluble in water, 
absolute alcohol, and other neutral solvents. Examples: glia- 
din (wheat), zein (corn), hordein (barley), kafirin (kafir corn). 

{e) Albuminoids. These are the simple proteins character- 
istic of the skeletal structures of animals (for which reason they 
are also called scleroproteins) and also of the external pro- 
tective tissues, such as the skin, hair, etc. None of these pro- 
teins is used for food in the natural state, but collagen when 
boiled with water yields gelatin. 

(/) Hi stones. Soluble in water, and insoluble in very dilute 
ammonia, and in the absence of ammonium salts insoluble 
even in an excess of ammonia ; yield precipitates with solutions 
of other proteins and a coagulum on heating which is easily 
soluble in very dilute acids. On hydrolysis they yield several 
amino acids, among which the basic ones predominate. The 
only members of this group which have any considerable im- 
portance as food are the thymus histone and the globin derived 
from the hemoglobin of the blood. 



PROTEINS 53 

(g) Protamins. These are simpler substances than the 
preceding groups, are soluble in water, not coagulable by heat, 
possess strong basic properties, and on hydrolysis yield a few 
amino acids among which the basic amino acids greatly pre- 
dominate. They are of no importance as food. 

II. Conjugated Proteins. Substances which contain the 
protein molecule united to some other molecule or molecules 
otherwise than as a salt. 

(a) Nucleo proteins. Compounds of one or more protein 
molecules with nucleic acid. Examples of the nucleic acids 
thus found united with proteins are thymo-nucleic acid (thy- 
mus gland), tritico-nucleic acid (wheat germ). 

ih) Glycoproteins. Compounds of the protein molecule 
with a substance or substances containing a carbohydrate 
group other than a nucleic acid. Example : mucins. 

(c) Phospho proteins. Compounds in which the phosphorus 
is in organic union with the protein molecule otherwise than 
in a nucleic acid or lecithin. Examples: caseinogen (milk), 
ovo\dtellin (egg yolk). 

{d) Hemoglobins. Compounds of the protein molecule with 
hematin or some similar substance. Example: hemoglobin of 
blood. (The redness of meat is due chiefly to the hemoglobin 
of the blood which the meat still retains.) 

(e) Lecitho proteins. Compounds of the protein molecule 
with lecithins or related substances. 

III. Derived Proteins. 

I. Primary protein derivatives. Derivatives of the protein 
molecule apparently formed through hydrolytic changes which 
involve only slight alterations. 

(a) Proteans. Insoluble products which apparently result 
from the incipient action of water, very dilute acids, or enzymes. 
Examples: casein (curdled milk), fibrin (coagulated blood). 

{b) Metaproteins. Products of the further action of acids 
and alkalies whereby the molecule is sufficiently altered to form 



54 CHEMISTRY OF FOOD AND NUTRITION 

proteins soluble in very \ycak acids and alkalies, V:)ut insoluble 
in neutral solvents. This group includes the substances 
which have been called " acid proteins," " acid albumins," 
" syntonin," "alkali proteins," " alkaU albumins," and 
*' albuminates." 

(c) Ccagulated proteins. Insoluble products which result 
from (i) the action of heat on protein solutions, or (2) the action 
of alcohol on the protein. Example : cooked egg albumin, or 
egg albumin precipitated by means of alcohol. 

2. Secondary protein derivatives. Products of the further 
hydrolytic cleavage of the protein molecule. 

(a) Proteoses. Soluble in water, not coagulable by heat, 
precipitated by saturating their solutions with ammonium 
sulphate or zinc sulphate. The products commercially known 
as " peptones " consist largely of proteoses. 

{b) Peptones. Soluble in water, not coagulable by heat, and 
not precipitated by saturating their solutions with ammonium 
sulphate or zinc sulphate. These represent a further stage of 
cleavage than the proteoses. 

(c) Peptids. Definitely characterized combinations of two 
or more amino acids. An anhydride of two amino acid radicles 
is called a " di-peptid " ; one having three amino acid radicles, 
a " tri-peptid " ; etc. Peptids result from the further hydro- 
lytic cleavage of the peptones. As was mentioned above, many 
peptids have also been made in the laboratory by the linking 
together of amino acids. 

Substances simpler than the peptones but containing several 
amino acid radicles are often called " polypeptids." 

Properties of Some Individual Proteins 

Albumins and globulins are very often associated, as, for 
example, in blood serum and in the cell substance. As a rule 
the albumins are the more abundant in animal fluids, while 



PROTEINS 55 

the globulins predominate over albumins in animal tissues and 
in plants. There appears to be no sharp dividing line between 
the albumins and the globulins. While the globulins are in- 
soluble in pure water, a water extract of animal tissue (muscle, 
for example) will contain, in addition to albumin, a considerable 
amount of globulin carried into solution by the salts present in 
the tissue, and if the salts are removed as completely as possible 
by dialysis, some of the globuhn still remains in solution ; sepa- 
rations based upon saturation with neutral salts are also apt 
to be unsatisfactory (Howell). 

Notwithstanding these diflficulties, a considerable number of 
individual albumins and globuHns have been isolated, purified, 
and analyzed. In ultimate composition they show a general 
similarity except that the albumins are richer in sulphur than 
the globulins. 

Several members of each group have also been studied to 
determine the kinds and amounts of amino acid radicles which 
they contain, with the results shown in the table on pages 60 
and 61. It is of interest to compare the amino acid make-up 
of typical proteins with their adequacy in nutrition. A few 
studies of tliis sort, notably those of Kauffmann with gelatin 
and Willcock and Hopkins with zein, had been made some years 
earUer, but much the greater part of our knowledge in this 
field is due to the recent investigations of Osborne and Mendel 
(191 1 et seq.). Rats have been chiefly used as the experimental 
animal. 

Egg albumin, perhaps the most familiar of all proteins and 
the one most often chosen to illustrate, in the laboratory, the 
properties of proteins in general, will be seen to yield no glycine 
but to furnish all the other usual amino acids in quite appreciable 
proportions. The feeding experiments show that with a diet 
adequate as regards all other factors animals may be maintained 
in normal nutrition and young animals may make normal 
growth with egg albumin as the sole protein food. 



56 CHEMISTRY OF FOOD AND NUTRITION 

Lactalbumin shows this same property in even greater degree. 
It appears to be the most efficient in supporting growth of all 
the proteins which have been studied, and this is believed to 
be due primarily to its high lysine content (see table beyond). 

Legumelin and leucosin have not yet been studied in feeding 
experiments of this kind, nor have such experiments been made 
with amandin or vicilin. 

Only preliminary feeding experiments not entirely success- 
ful as regards growth have been reported for legumin, phaseolin, 
and vignin; but each of the other three vegetable globulins 
shown — edestin, excelsin, and glycinin — has been found to 
suffice for maintenance and normal growth when fed as the 
sole protein in a diet adequate in other respects.* In fact 
Osborne and Mendel have kept one family of rats through three 
generations with edestin as a sole protein food. 

Glutelins and the alcohol-soluble proteins (prolamins) are im- 
portant as constituents of the cereal grains. The best-known 
examples of the respective groups are glutenin and gliadin of 
wheat flour. These proteins resemble each other in ultimate 
composition, but differ not only in solubilities, but also in their 
cleavage products. They are much the most important of the 
proteins of the wheat kernel, the gliadin making up about 50 
per cent and the glutenin about 40 per cent of the total protein 
present. The gliadin and glutenin together constitute the glu- 
ten of wheat flour. 

Glutenin (wheat glutelin) and maize gliitelin have each been 
shown capable, in the rat-feeding experiments cited above, of 
meeting the requirements not only of maintenance but also of 
normal growth when fed as the sole protein food in diets adequate 
in other respects. 

Gliadin, hordein, and the prolamin of rye, when fed singly in 
the same manner, are found capable of maintaining grown rats 

* Factors necessary to make a diet adequate will be discussed in Chapters XII 
and XIII, where experiments upon growth will be considered in greater detail. 



PROTEINS 57 

but not of supporting normal growth. Zein, fed alone in similar 
experiments, did not suffice either for maintenance or for growth. 
Osborne and Mendel concluded from these experiments that 
the failure even to maintain the grown animals was due to the 
absence of tryptophane ; while the failure of the rats to grow 
on gliadin, hordein, or rye prolamin was due to the fact that 
these proteins either lack lysine or contain it in insufficient quan- 
tity. This interpretation was confirmed by later experiments 
in which they found that adding tryptophane to the zein food 
made it adequate for maintenance and adding lysine to the 
gliadin food made it adequate to support growth. 

Gelatin, the only member of the albuminoids (scleroproteins) 
which is of practical importance as food, has long been known to 
be unable to support protein metabolism when fed as the sole 
protein food. This inadequacy now appears to be due to the 
absence of tryptophane and tyrosine and perhaps in part also to 
the fact that some of the other amino acids, cystine and histidine, 
are furnished by gelatin in only very small proportion. As 
early as 1905 Kauffmann tried the experiment of living upon a 
diet in which gelatin was the sole protein, but was supplemented 
by additions of tyrosine, tryptophane, and cystine. So far as 
could be determined by a short experiment the addition of these 
amino acids seemed to make good the deficiencies of the 
gelatin. 

Nucleoproteins are the characteristic proteins of cell nuclei, 
and are therefore especially abundant in the highly nucleated 
cells of the glandular organs, such as the thymus, the pancreas, 
and the liver. They are compounds of simple proteins with 
nucleic acid or nuclein. The chemical nature of the latter and 
their behavior in metabolism will be considered in Chapter V. 

Phospho proteins occur especially in milk and eggs, which ob- 
viously function in nature to provide the material for growth and 
development of new animal tissue. The phosphorus, while prob- 
ably present in the form of a more or less modified phosphoric 



58 



CHEMISTRY OF FOOD AND NUTRITION 



acid radicle, appears to be more closely bound in these than in 
the nucleoproteins. Casein of milk and the vitellin of egg yolk 
(ovo-vitellin) are the most prominent members of the group. 
These are sometimes classed with simple proteins under the 
name nucleo-albumins. Phosphoprotein preparations show on 
analysis small amounts of iron, which has usually been neglected 
as an impurity but which is not improbably an essential con- 
stituent. 

Casein and ovo-vitellin fed singly as the sole protein of the 
ration in the experiments by Osborne and Mendel described 




Fig. I. — Showing typical curves of growth of rats on diets otherwise similar and 
adequate but containing in each case only a single protein, casein, gUadin, or zein. 
Courtesy of Dr. L. B. Mendel and the Journal of the American Medical Association. 

above have each been found capable of supporting both main- 
tenance and normal growth, as their amino acid make-up and 
their place in nature would lead us to expect. The curves in 
Fig. I illustrate the rapid growth on casein as compared with 
the very slow growth on gliadin and the loss of weight when 
zein was the sole protein food. The rations were alike except 



PROTEINS 59 

for the nature of the protein fed ; the percentage of protein 
in the ration was the same in each case. 

It will be seen that the rat receiving casein grew over 200 
grams in 140 days while the one fed with gUadin grew only 20 
grams during the same period. The third rat, which had been 
growing rapidly on mixed food, began at once to lose weight when 
put on a ration of which zein was the sole protein. 

Hemoglobins^ consisting of combinations of simple proteins 
with coloring matter, serve as carriers of oxj^gen from the air 
to the tissues. On boiling or heating with acids or alkahes they 
are spht into their constituent parts : for example, ordinary 
hemoglobin \aelds about 4 per cent of hematin, C32H32N4Fe04, 
and a residue of globin which was formerly considered a globulin 
but is now assigned to the histone group. 

Proteoses and peptones are products derived from other pro- 
teins by digestion or by simple hydrolysis. They are soluble 
in water and not coagulated by boihng their aqueous solutions. 
No sharp line can be draw^n either between proteoses and pep- 
tones, or between peptones and the simpler nitrogen compounds 
which result from prolonged digestion. As the terms are gen- 
erally used, peptones may be considered as the products of diges- 
tion or hydrolysis which still show the usual color reactions of 
proteins and are precipitated by strong alcohol ; but are not 
precipitated by saturation of their solutions with zinc or ammo- 
nium sulphate, as is the case with proteoses. Proteoses (albu- 
moses) are intermediate products between metaprotein and pep- 
tones. In addition to the protein reactions shown by peptones, 
the proteoses are precipitated from aqueous solutions at ordinary 
temperatures by adding acetic acid and potassium ferrocyanide, 
or by saturating the solution \vith zinc or ammonium sulphate. 

The term " peptone " was formerly apphed to all digestion 
products not coagulated by boiling, and is still popularly used 
in the same sense, the best commercial " peptones " consisting 
largely of proteoses. 



6o 



CHEMISTRY OF FOOD AND NUTRITION 





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Z XI E 



62 CHEMISTRY OF FOOD AND NUTRITION 

Relation between Chemical Constitution of the Proteins and 
Their Food Value 

Several facts bearing upon the relation between the feeding 
values of individual proteins and their amino acid make-up have 
been cited in the preceding pages. The subject is of great im- 
portance and is now under active investigation. Since the 
experimental facts are still being determined, any attempt to 
generalize broadly at this point would be premature. A few 
important conclusions may, however, be deduced from the facts 
already given. 

Glycine, although an essential constituent of body tissue, need 
not be furnished by the food, for several proteins which do not 
yield glycine on hydrolysis have been shown to be adequate when 
fed as sole protein of an experimental ration. It appears 
therefore that supplies of glycine fully adequate to meet all 
normal needs may be formed within the body itself. 

Tryptophane, on the other hand, apparently must always be 
supplied to the animal body ; food furnishing no tryptophane 
has always proven inadequate even for maintenance of full- 
grown animals. Apparently the animal body is unable to make 
tryptophane (or at least to make it at the rate required for 
normal metaboHsm) and proteins lacking the tryptophane radicle 
must be regarded as always inadequate as a sole protein food. 

Lysine, again, is especially important in connection with 
growth. Proteins which yield little, if any, lysine (and which 
are otherwise adequate in their amino acid make-up) appear 
to suffice as the sole protein food in the maintenance of full- 
grown animals (rats) but not to support a normal growth of 
the young. 

As regards the influence of the presence or absence of glycine, 
lysine, and tryptophane radicles in the protein molecule, it 
seems possible to correlate the chemical structure and the 
nutritive value of the proteins quite definitely. In estabhsh- 



PROTEINS 



63 



ing this correlation, Osborne and Mendel have made one of the 
most important advances in the entire development of the 
chemistry of food and nutrition. 

That the inadequacy of zein for maintenance is essentially 
due to the lack of tryptophane, they demonstrated by feeding a 
ration with zein as sole protein but with tryptophane added. 
This mixture permitted maintenance without growth (rat 1892, 
middle portion of Fig. 2). Then by the addition of lysine to 
the zein and tryptophane diet they induced normal growth as 
shown by the continuation of the weight curve of rat 1892 at 




urves of Growth =>" Zein + Amino Acids 



iphane 




Fig. 2. — Showing the effect of adding tryptophane or tryptophane and lysine to 
a diet containing zein as the sole protein (compare Fig. i, page 58). Courtesy of 
Dr. L. B. Mendel and the Journal of the American Medical Association. 

the right of Fig. 2. In another case (rat 1773, at the left of 
Fig. 2) a rat which was rapidly losing weight on the zein diet 
was restored to a condition of normal growth by the addition 
of tryptophane and lysine to the food. 

As Mendel expresses it : " If we analyze the situation as 
revealed in the charts of some actual experiments, it becomes 
apparent that both lysine and tryptophane are unquestionably 
necessary as constructive units in growth. The decline brought 
about by the zein food can be stopped by the addition of trypto- 
phane, as such, to the diet. This results in maintenance ; but 
no growth ensues until lysine also is added." 

Osborne and Mendel also showed that the addition of lysine 
to the gliadin ration made it adequate to support normal 



64 



CHEMISTRY OF FOOD AND NUTRITION 



growth. They have also shown that retardation of growth may 
sometimes be due to restricted intake of some amino acid other 
than lysine. 

In the experiments above described the rations always con- 
tained a liberal amount (usually i8 per cent) of protein. If, 
on the other hand, the percentage of protein in the food be 



020 



280 



240 






.S 120 



.90 



40 







1 


/ 


/ 


^3-.; . /^...^ 




Case 


in T v^yo / 












/ 


/ 








Y 


r 




/ 




¥ 

V 


/ 




1 1 

M 


/ 


{ 


j/ 


1 
1 

f\ 

1 J 1 




1 1 




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1 


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y^ 


40 Days 

< ■> 









Fig. 3. — Showing that the insufficiency of a low-casein diet was essentially due 
to its relative deficiency in cystine. Courtesy of Dr. L. B. Mendel and the Journal 
of the American Medical Association. 

sufficiently reduced, the growth may be retarded even though the 
protein be of a kind which is entirely adequate when liberally 
fed. Thus on a ration containing g per cent of casein the rats 
grew only about half as rapidly as when they received 18 per 
cent ; * and in this case the limiting factor was not lysine but 

* On account of the very different rates of growth, not to mention other differ- 
ences between the species, one must not attempt to apply the quantitive data of 
the rat-feeding experiments directly to the problem of protein requirement in man. 



PROTEINS 65 

cystine, for the addition of cystine to the low-casein diet in- 
duced a normal rate of growth which was immediately checked 
when the cystine was v/ithdrawn and resumed when the cystine 
was again added to the ration (Fig. 3). 

In all of -the experiments cited thus far each ration contained 
only a single isolated protein. This is the ideal condition for 
the experimental comparison of individual proteins, but is quite 
different from ordinary or "practical" conditions, since our 
common protein foods all contain mixtures of proteins, so that 
even if only a single article of food were consumed the diet 
would still furnish more than one protein at a time. By feed- 
ing definite mixtures of pure proteins Osborne and Mendel have 
beautifully demonstrated the way in which proteins supple- 
ment each other in nutrition. Thus zein alone is, as we have 
seen, always inadequate as a sole protein food ; lactalbumin is 
adequate when fed in sufficient quantity but when constituting 
only 4.5 per cent of the food mixture of rats it supports only 
slow growth; but a food mixture containing 4.5 per cent of 
lactalbumin and 13.5 per cent of zein supports growth at a 
fully normal rate (Fig. 4). This shows that a relatively small 
amount of lactalbumin (one fourth of the protein fed) sufficed 
to furnish the amino acid groups which the zein lacked. It 
shows also that zein, which when fed as a sole protein is insuf- 
ficient even for maintenance, is able as a constituent of a proper 
food mixture to take part in supplying the materials for growth, 
to such an extent as to more than double the growth-rate. Thus 
zein, although inadequate for either maintenance or growth when 
isolated and fed alone, may nevertheless take an important 
part in both maintenance and growth when fed as a part of a 
proper mixed diet. Moreover it may not even be necessary to 
resort to a mixture of food materials in order to make good the 
deficiencies of the individual incomplete protein. Corn fmaize) 
itself, along with zein, contains an almost equal amount of 
another protein, maize glutelin, which Osborne and Mendel 



66 



CHEMISTRY OF FOOD AND NUTRITION 



have shown to be capable of supporting a normal rate of growth 
— not to mention the proteins in the embryo of the maize 
kernel which appear to have a still higher nutritive efficiency 
(Hart and Humphrey; McCollum and Davis). 

Thus it is plain that the mixtures of proteins contained in 
different articles of food as wc cat them do not differ in such a 



240 









/ 


^ 








^, 


/ 










/ 










V 


¥/ 














"jj 




-^ 


f 




. ■ao 


A.^ 
^ 








jo^ 


\y^ 




40 Days 
c > 





•5 120 

i~ 
-c: 

•^ 30 



Fig. 4. — Showing the efficiency of lactalbumin as a supplement to zein, and also 
that zein may take an important part in growth although zein alone is inadequate 
either for growth or maintenance. Courtesy of Dr. L. B. Mendel and the Journal 
of the American Medical Association. 

striking way as do the individual proteins when isolated and 
fed singly ; but neither is it true that the proteins of different 
articles of food are equivalent for all practical purposes. Hart, 
McCollum, and their associates have shown that the natural 
protein mi.xture of milk is more efficient than an equal weight 
of the mixed proteins of wheat or corn (maize) both for the sup- 
port 01 growth in young animals (pigs) and as food for the pro- 



PROTEINS 67 

duction of milk in dairy cattle. While it is always possible that 
in comparisons between natural food materials the results may 
be influenced by differences in the unknown food constituents 
which may be present, yet in the cases here cited it is probable 
that the differing efficiencies ascribed to milk and grain proteins 
are mainly due to the same differences of chemical constitution 
("amino acid make-up") to which are attributable the striking 
results obtained in the experiments previously cited in which 
isolated foodstuffs were fed. 

REFERENCES 

Abderhaldex. Lehrbuch der Physiologische Chemie. 

Fischer. Untersuchungen iiber Aminosauren, Polypeptide und Proteine. 

Ceiling. The Nutritive Value of the Diamino-Acids occurring in Proteins 
for the Maintenance of Adult Mice. Journal of Biological Chemistry, 
Vol. 31, page 173 (1917)- 

Hart and Humphrey. The Relation of the Quality of Proteins to Milk 
Production. Journal of Biological Chemistry, Vol. 21, page 239 (1915) ; 
Vol. 26, page 457 (1916) ; Vol. 31, page 445 (1917)- 

Hammarsten.. Textbook of Physiological Chemistry. 

Hawk. Practical Physiological Chemistry. 

Jones. The Nucleic Acids; their Chemical Constitution and Physiological 
Conduct. 

Kossel. Lectures on the Herter Foundation. The Proteins. Bulletin 
of the Johns Hopkins Hospital, Vol. 23, page 65 (1912). 

Mann. Chemistry of the Proteids. 

Mathews. Physiological Chemistry. 

McCoLLUM. The Value of Cereal Proteins for Growth. Journal of Bio- 
logical Chemistry, Vol. 19, page 323 (1914). 

!McCoLLUM AND Davis. Nutrition with Purified Food Substances. Jour- 
nal of Biological Chemistry, Vol. 20, page 641 (1915); The Cause of 
the Loss of Nutritive Efficiency of Heated Milk, Ibid., Vol. 23, page 

247 (1915)- 

Mendel. Nutrition and Growth. The Harvey Society Lectures for 
1914-1915, page loi ; and Journal of the American Medical Associa- 
tion, Vol. 64, page 1539 (1915). 

Mitchell. Feeding Experiments on the Substitution of Protein by 
Definite Mixtures of Isolated Amino Acids. Journal of Biological 
Chemistry, Vol. 26, page 231 (1916). 



68 CHEMISTRY OF FOOD AND NUTRITION 

Osborne. The Vegetable Proteins. 

OsBORNK. Die Pflanzenproteine. Ergebuisse der Physiologic, Vol. lo, 
pages 47-215 (1910)- 

Osborne and Mendel. Feeding Experiments with Isolated Food Sub- 
stances. Carnegie Institution of Washington, Publication No. 156 
(Parts I and II) and a series of subsequent articles : Journal of Biological 
Chemistry, Vol. 12, page 473; Vol. 13, page 233; Vol. 17, page 325 ; Vol. 
18, page i; Vol. 20, page 351; Vol. 22, page 241; Vol. 25, page i; 
Vol. 26, pages I, 293; Vol. 29, page 69 (1911-1916). Examine also 
the later issues of this Journal for papers published subsequently to 
the compiling of this list. 

Osborne, Van Slyke, Leavenworth, and Vinograd. Some Products 
of Hydrolysis of Gliadin, Lactalbumin, and the Protein of Rice. Jour- 
nal of Biological Chemistry, Vol. 22, page 259 (1915). 

Plimmer. Chemical Constitution of the Proteins, I and II. 



CHAPTER IV 

ENZYMES AND DIGESTION 

The carbohydrates, fats, and proteins as they exist in foods* 
are in most cases not of a nature to be used by the body tissues 
in the exact form in which they are eaten, but must usually 
undergo more or less alteration in the digestive tract to fit them 
for absorption and utilization. In so far as the changes which 
the food undergoes in the alimentary tract are chemical they 
are brought about mainly by the action of digestive enzymes; 
but the efficiency of the digestive process is also largely de- 
pendent upon the mechanical factors of digestion which there- 
fore will also be briefly considered in this chapter. 

Historical 

The idea that changes comparable to fermentation are in- 
volved in the processes of digestion apparently originated with 
von Helmont about 300 years ago. Sylvius, half a century 
later, cited alcohoUc and acetous fermentations to illustrate the 
type of process by which he believed the foodstuffs to be digested. 
Descartes held that as the result of a peculiar fermentation there 
was generated in the stomach "an acid of great potency, com- 
parable to nitric acid." From the standpoint of our present 
knowledge these early scientists appear to have made con- 
siderable progress toward a correct interpretation of the digestive 
process; but in their own times, before the beginning of the 

* A table showing percentages of proteins, fats, and carbohydrates in foods is 
given in Appendix B. 

69 



70 CHEMISTRY OF FOOD AND NUTRITION 

scientific development of organic or physiological chemistry, 
the views which they advanced appeared hazy and unscientific 
compared with those of the physiologists who were studying 
digestion from the mechanical point of view and by supposedly 
exact methods. Thus Dr. Archibald Pitcairn (1652-1713) 
proposed to explain gastric digestion, " without the aid of a 
Daemon or a Stygian Liquor," as due entirely to the triturating 
action of the stomach, the power of whose muscular walls he 
estimated as " equal to 12,951 pounds " (Gamgee). 

The view that the digestion of food in the stomach is due 
solely to the mechanical action of the stomach walls was refuted 
by Reaumur, working with birds, and by Stevens, who experi- 
mented with a man who was accustomed to swallow small stones 
and regurgitate them at will. In Stevens' experiments this man 
swallowed hollow silver balls filled with food and perforated to 
permit access of the gastric juice but strong enough to resist 
the muscular contractions of the stomach walls. Food thus 
introduced was found to undergo digestion in the stomach al- 
though it was entirely protected from the triturating action of 
the stomach walls. Furthermore Stevens found that gastric 
juice obtained from a dog was able to digest meat outside of the 
stomach. At about the same time Spallanzani also showed 
clearly that gastric juice can act outside of the body. In addi- 
tion, he pointed out its antiseptic properties and emphasized the 
difference between the digestive process and that of alcoholic, 
acid, or putrefactive fermentation. About fifty years after 
the work of Spallanzani came the classical observations (1825- 
1833) of Dr. Beaumont upon Alexis St. Martin, who, as the result 
of a gunshot wound, was left after recovery from his injury 
with a gastric fistula which permitted both the collection of 
human gastric juice and the direct observation of the processes 
going on in the stomach of a healthy man "active, athletic, and 
vigorous, exercising, eating, and drinking, like other healthy 
and active people." Dr. Beaumont's full and interesting ac- 



ENZYMES AND DIGESTION 7 1 

count of his experiments with St. Martin ^ greatly extended 
the knowledge both of the muscular behavior of the stomach 
and of the conditions governing the secretion of the gastric 
juice and the " chymification " of the food in the stomach. The 
year after the publication of Beaumont's observations, Eberle 
showed - that by extracting the mucous membrane of the 
stomach with dilute hydrochloric acid he could obtain an 
artificial juice which showed the same digestive action which 
Spallanzani and Beaumont had observed with the natural se- 
cretion, and two years later Schwann ^ concluded that gastric 
juice owed its pecuUar activity to a substance presumably dif- 
ferent from any substance previously known and to which he 
gave the name pepsin. Schwann did not claim to have isolated 
this peculiar substance in a pure state but did effect a partial 
separation. Subsequently several other investigators attempted 
to isolate pepsin. 

Attempts to Determine the Chemical Nature of Enzymes * 

In 1902 Pekelharing prepared what has generally been re- 
garded as probably the purest pepsin of which we have record. 
This product contained carbon, hydrogen, nitrogen, and sul- 
phur in proportions within the range of variation found among 
ordinary proteins.f It also behaved like ordinary proteins in 
the xanthoproteic test and Millon reaction and in showing the 
presence of the tryptophane group. 

1 W. Beaumont. Experiments and Observations on the Gastric Juice and the 
Physiology of Digestion. Plattsburg, 1833. 

2 Eberle. Physiologic der Verdauung nach Versuchen. Wiirzburg, 1834. 

' Schwann. Ueher das Wesen der Vcrdauungsproccsse. Miiller's Archiv, 1836, 
pages 90-138. 

* Those students not yet familiar with the names of the common enzymes 
should perhaps read first the sections on classification and terminology below. 

t A small amount of chlorine shown by Pekelharing's preparation was later 
found by Dezani to be not an essential constituent but probably due to incomplete 
removal of the hydrochloric acid with which pepsin is associated in the gastric juice. 



72 CHEMISTRY OF FOOD AND NUTRTTTON 

Dezani, in igio, carried forward Ihe work upon Ihc chemical 
nature of pepsin by preparing what was beheved to be a sub- 
stantial duplicate of Pekelharing's product and submitting this to 
hydrolysis, followed by search for individual hydrolytic products 
according to the methods which had recently been developed in 
the study of the structure of the proteins. He demonstrated the 
presence of leucine, tyrosine, arginine, histidine, and lysine and 
also found evidence of other amino acids which the limitations 
of his material and methods did not permit him to identify. 

Thus pepsin as prepared by Pekelharing and by Dezani is a 
nitrogenous material not identical with any other known sub- 
stance but complying with the criteria of our present concep- 
tion of a protein in elementary composition, in color reactions, 
and especially in yielding the familiar amino acids upon hy- 
drolysis. Recent studies by Aldrich also indicate that the 
chemical nature of pepsin is that of a protein. 

It must be borne in mind that the criteria of purity usually 
appHed in chemical investigations are not applicable to enzyme 
preparations because of their colloidal nature and the readi- 
ness with which their characteristic properties are destroyed. 
Yet in view of the fact that, with very few if any excep- 
tions, the changes by which the organic foodstuffs are pre- 
pared for absorption in the digestive tract and are utiHzed in 
the body tissues are dependent upon the presence of enzymes the 
material for whose synthesis must in the long run be furnished 
by food, we should not be deterred by the inherent difficulties 
and uncertainties of the subject from the study of such evidence 
regarding the chemical nature of the enzymes as can be obtained ; 
nor are we at present quite so much in the dark as the state- 
ments in most textbooks would seem to indicate. 

Several years earlier than Pekelharing's work on pepsin, Os- 
borne ^ had published an investigation of the chemical nature 

1 T. B. Osborne. Journal of the American Chemical Society, Vol. 17, page 587 
(1895) ; Vol. 18, page 536 (1896). 



ENZYMES AND DIGESTION 73 

of diastase (malt amylase), which may be regarded as marking 
the beginning of our modern knowledge in this field. From this 
work it appeared that the enzymic activity is a property of a 
definite fraction of the protein material of the malt, or in other 
words that the enzyme is protein in its chemical nature. Al- 
though criticized by some, Osborne's findings have been con- 
firmed by the most recent investigations. Since space permits 
here only the discussion of those enzymes which are directly 
concerned in digestion, the reader must be referred to the 
original papers for an account of Osborne's methods and results. 

Of the two amylases concerned in the digestive process, 
ptyalin of saliva and amylopsin of the pancrei'^tic juice, only 
the pancreatic amylase has been studied by modern methods 
with reference to its chemical nature. 

In an investigation ^ in which the attempts at purification 
were guided and their success largely judged by quantitative 
determinations of the starch-digesting action of the products 
there was developed a method of purification which in nu- 
merous independent experiments yielded a product that was 
not only extraordinarily active in the hydrolysis of starch but 
was essentially uniform both in digestive activity and in chemi- 
cal nature. This result strongly suggests that the product was 
not merely an indefinite mixture but represented at least some 
approximation toward an actual isolation of the enzyme. These 
preparations show the composition and color reactions of 
typical proteins and, hke Osborne's malt amylase, the material 
when heated in water solution yields an albumin coagulum and 
a proteose or peptone which remains in solution. Moreover, on 
hydrolysis the material yields the same groups of amino acids 
which are yielded by typical proteins such as casein, which it 
also resembles in elementary composition. 

While the chemical nature of the lipases of the digestive tract 

* Journal of the American Chemical Society, Vol. a, page 1195; Vol. 34, page 
1104; Vol. 35, page 1790. 



74 CHEIMISTRY OF FOOD AND NUTRITION 

has not been studied, Falk and Sugiura have shown that the 
purified Hpase preparations made from castor beans are, Uke 
the proteases and amylases above mentioned, essentially pro- 
tein material.* 

The materials obtained in attempts to isolate enzymes are 
here called merely products or preparations ; it is not stated 
that any enzyme has been perfectly separated and purified. As 
already explained, the familiar criteria of purity are not appli- 
cable to these unstable colloidal substances. It is possible that 
the enzymes in the purified preparations mentioned above may 
still be mixed with considerable amounts of other substances, 
and it has ev^n been suggested that the protein material of 
which the above-mentioned enzyme preparations are chiefly 
composed may be present only as a carrier and that the actual 
enzyme may be a substance of a different nature. There is, 
however, no direct evidence in favor of this suggestion. The 
facts now available make it altogether probable that the typical 
enzymes concerned in the utihzation of the foodstuffs either are 
modified proteins or contain protein as an essential component. 
In this case the food protein must furnish material for body 
enzymes as well as for body tissue. 

Classification and General Properties of Enzymes 

The word "enzyme" (from the Greek "in yeast") was intro- 
duced by Kiihne as a general designation for the substances 
formed in plants or animals which had previously been called 

* Recently Falk has suggested that the lipolytically active grouping is the 
tautomeric enol-lactim form of the peptide linking which becomes inactive on 
rearrangement to the keto form. Experiments testing this view resulted in the pro- 
duction of lipolytically active substances by the action of alkali on castor bean 
globulin, casein, and gelatin. Further confirming evidence was obtained on study- 
ing the ester-hydro lyzing action of glycine, glycyl-glycine, and hippuric acid at 
different hydrogen ion concentrations. Falk holds that "given a definite chemical 
grouping, the nature of which has been indicated, and which may be present in 
different classes of substances, certain definite lipolytic actions will result." 



ENZYMES AND DIGESTION 75 

"soluble" or "unorganized" ferments to distinguish them 
from " organized " ferments (fermentation organisms). As 
more and more of the acti\dties previously regarded as char- 
acteristic of organisms have been found to be due to enzymes, 
the conception of enzyme action has broadened until now the 
term enzyme is apphed by most writers to all organic catalysts 
formed in plant or animal cells. Those which are ordinarily 
secreted from the cell and exert their activities outside of it 
(as in the case of the digestive ferments) are sometimes called 
extracellular enzymes, and those which normally perform their 
functions within the cells in which they are formed (as in yeast 
or in muscle cells) may be called intracellular enzymes even 
though it be possible by artificial means to cause them to act 
independently of living matter. Although each enzyme is 
generally supposed to be a definite chemical substance, the 
identification and classification of enzymes are based upon the 
changes which they bring about. Some of the better-known 
groups of enzymes are as follows : 

1. The hydrolytic enzymes. 

a. Proteolytic or protein-splitting enzymes. 

b. Lipolytic or fat-splitting enzymes. 

c. Amylolytic or starch-splitting enz3^mes. 

d. Sugar-splitting enzymes. 

2. The coagulating enzymes, such as thrombin or thrombase 
(the fibrin ferment), and rennin, which causes the clotting of milk. 

3. The oxidizing enzymes, or " oxidases " (which, if the oxi- 
dation be accompanied by a splitting off of amino groups, may 
be called " deamidizing " or " deaminizing " enzymes). 

4. The reducing enzymes or " reductases." 

5. Those which, like the zymase of yeast, produce carbon 
dioxide without using free oxygen. 

* 6. Enzymes causing a breaking down of a larger into a smal- 
ler molecule of the same composition, as in the production of 
lactic acid from glucose. 



76 CHEMISTRY OF FOOD AND NUTRITION 

7. Enzymes causing chemical rearrangement without break- 
ing down of larger into smaller molecules, " mutases." 

Terminology of the hydrolytic enzymes. — Except in so far 
as some familiar enzymes continue to be known by their old 
estabhshed names (pepsin, rennin, trypsin, etc.), scientific 
usage now generally follows the suggestion of Duclaux that 
each hydrolytic enzyme be designated by a name indicating the 
kind of substance on which it acts, together with the sufl5x ase. 
Thus starch-splitting enzymes are called amylases; fat-splitting 
enzymes, lipases; protein-splitting enzymes, proteases. The 
name showing the activity of the enzyme is often preceded by 
an adjective to indicate its source ; e.g. salivary amylase (ptya- 
lin), pancreatic amylase (amylopsin). Such designation does not 
necessarily imply that the amylase found in the saliva either is or 
is not the same substance as the amylase of the pancreatic juice. 

In discussions of enzyme action the substance on which the 
enzyme acts is sometimes called the substrate. 

Within the cell producing it an enzyme often exists in an 
inactive form known as the zym-ogen or antecedent of the active 
enzyme. The zymogen may be stored in the cell in the form of 
material which is converted into active enzyme at the time of 
secretion, or the secretion may be poured out with the zymogen 
not yet completely changed to active enzyme, or sometimes in a 
form which requires the presence of some other substance in 
order to render it active. In this case the latter substance is 
said to activate the enzyme. 

Influence of hydrogen ion concentration. — The activity of 
most enzymes is largely dependent upon the exact acidity or 
alkalinity of the medium. This is now usually expressed in 
terms of hydrogen ion concentration. Thus a normal solution 
of hydrochloric acid would contain, if the HCl were completely 
ionized, i gram of hydrogen ions per liter ; and in a thousandth- 
normal solution in which the ionization actually is almost com- 
plete (actually about 99 per cent of the HCl in such a solution 



ENZYMES AND DIGESTION 77 

is ionized at ordinary temperatures) the concentration of hy- 
drogen ions is o.ooi gram per liter or i x io~^. Pure water, 
according to the usually accepted estimates, has a hydrogen 
ion concentration of i x lo"'' and the same concentration of 
hydroxyl ions. Thus water which is pure and strictly neutral 
may also be regarded as being equivalent to a ten-miUionth- 
normal acid and at the same time a ten-millionth-normal alkali. 
In order to avoid cumbersome numbers Sorensen has proposed 
to indicate hydrogen ion concentration by writing the negative 
exponent as a whole number, e.g. in the case of pure water 
Ph"^ = 7-0 ; in thousandth-normal hydrochloric acid Ph"*" = 3.0. 
Thus according to the Sorensen notation, generally indicated 
by the use of the symbol Ph^, a number lower than 7 shows 
acidity and the more acid the solution the lower the number ; 
a number higher than 7 shows alkalinity and the greater the 
alkalinity the higher the Pg"*" number, since this is the negative 
exponent of the hydrogen ion concentration. 

It must be remembered that the Sorensen exponent, or Ph"*" 
number, varies with the hydrogen ion concentration not arith- 
metically but logarithmically : i x io~® = Ph"*" 6.0 ; 2 X io~® 

= Ph" 5-7. 

f The hydrogen ion concentrations most favorable to the action 
of certain well-known enzymes have recently been measured 
with the following results : 

Enzyme Optimitm H Ion Concentration as Ph+ 

(Nelson) 

(Okada) 

when acting on fibrin (Long) 

when acting on casein (Long) 

(Sherman and Thomas) 

Activity of the Digestive Enzymes 

That the typical digestive enzymes are very pronounced 
catalysts may be judged from the relatively large amounts of 



Invertase (Sucrase) 


4-4 


Pepsin . . . 


1-5 


Trypsin . . . 


8.0-8.3 


Trypsin . . . 


5-6-6.3 


Malt amylase 


4-4 



78 CHEMISTRY OF FOOD AND NUTRITION 

material which they are capable of digesting under favorable 
conditions. Thus Hammarsten's rennin coagulated 400,000 to 
800,000 times its weight of casein ; Petit described a pepsin 
powder which dissolved 500,000 times its weight of fibrin form- 
ing 1000 times its weight of peptone; the pancreatic amylase 
preparation of Sherman and Schlesinger digested 2,000,000 
times its weight of starch with the production of 1,200,000 times 
its weight of maltose. 

A catalyzer is usually considered to alter the velocity of a 
reaction but not to initiate it. Thus hydrogen peroxide de- 
composes spontaneously into water and oxygen. In a pure 
aqueous solution this change goes on slowly, but it is very greatly 
accelerated by the presence of a minute amount of colloidal 
platinum. Blood and tissue extracts contain enzymes which 
accelerate the decomposition of hydrogen peroxide apparently 
in much the same way as does platinum, and the present tend- 
ency is to regard the enzymes generally as acting quite like the 
inorganic catalyzers in altering by their presence the velocity 
of certain reactions. Some of the best-known enzyme actions, 
however, fit into this view only theoretically ; for if the enzyme 
be considered as simply accelerating a reaction already taking 
place, it must also be considered that in the absence of the 
enzyme the reaction is so slow that it cannot be demonstrated. 

It may perhaps be asked why, if enzymes act by catalysis, 
there should be any limit to the amount of substrate which the 
enzyme can hydrolyze. One reason that enzymes cannot hy- 
drolyze infinite amounts of substrate is that they are them- 
selves unstable organic substances which undergo decomposition 
when kept in solution. In most cases the purer the enzyme the 
more rapidly its solutions lose their activity. Another reason 
that an enzyme does not continue to hydrolyze substrate 
indefinitely is that the reaction is progressively retarded by 
the accumulation of the products formed. 

The activity of an enzyme may be stopped, even when all 



ENZYMES AND DIGESTION 



79 



other conditions are favorable, by the accumulation of the prod- 
uct of its action ; and in certain circumstances the action of 
the enzyme may be reversed so as to accelerate a change in the 
opposite direction to that in which it ordinarily acts. Thus 
Croft Hill showed it to be possible to reverse the ordinary action 
of maltase so as to make it bring about a conversion of mono- 
into di-saccharide ; Pottevin synthesized triolein by means of 
the pancreas ferment, and Taylor and others have demonstrated 
a partial reversion of the tryptic digestion of proteins. While 
the exact significance of these experiments upon the reversi- 
biUty of the actions brought about by the digestive enzymes has 
been questioned, there seems to be no doubt that hydrolytic 
enzymes are widely distributed in active cells and that many of 
the transformations which take place in the course of the me- 
tabolism of the foodstuffs in the body are best explained on the 
ground of the reversibility of enzyme action. Consideration of 
the tissue enzymes will be left until the study of the fate of the 
foodstuffs in metaboUsm is taken up. At this point it may 
be convenient to summarize in tabular form the occurrence 
and action of the chief digestive enzymes. 



SxHiiMARY OF Chief Digestive Enzymes 



Act on Car- 
bohydrates 



Enzymes Where Chiefly Found 

Ptyalin (salivary Salivary secretions 

amylase) 
Amj'lopsin (pan- Pancreatic juice 

creatic amj-lase) 
Invertase Intestinal juice 

(Sucrase) 



Action 



Act on Fat 



Maltase 
Lactase 

Lipases 



Intestinal juice 
Intestinal juice 

Gastric (?) and 
pancreatic 
juices 



Converts starch to 

maltose 
Converts starch to 

maltose 
Convert ; sucrose 

to glucose and 

fructose 
Converts maltose 

to glucose 
Converts lactose 

to glucose and 

galactose 
Split fats to fatty 

acids and gb'c- 

erol 



8o 



CHEMISTRY 01- FOOD AND NUTRITION 



Summary of Chief Digestive Enzymes {Continued) 



Enzymes 


Where Chiefly Found 


[Action 




Pepsin 


Gastric juice 


Splits proteins to 
proteoses and 
peptones 


. 


Trypsin 


Pancreatic juice 


Splits proteins to 


Act on Pro- 
teins 






proteoses, pep- 
tones, polypep- 
tids, and amino 
acids 




Erepsin 


Intestinal juice 


Splits peptones to 
amino acids and 
ammonia 



With this brief sketch of the nature and action of the diges- 
tive enzymes, the adequate discussion of which would require 
a volume in itself, we may now pass to a review of the digestive 
process, following the course of the food through the human 
alimentary tract and noting briefly both the mechanical and 
chemical treatment to which it is subjected. 



Salivary and Gastric Digestion 

Since the muscular movements of the digestive tract, par- 
ticularly of the stomach when empty, play an important part 
in bringing about the sensations which lead to the taking of 
food, it may be well to note at this point the results obtained 
by Cannon and Washburn in their recent investigation of 
hunger. Lest hunger be confused with appetite, it is essential 
to clearness that these terms be defined. Some consider that 
the two experiences differ only quantitatively, appetite being 
regarded as a mild state of hunger; but Cannon and Wash- 
burn hold that hunger and appetite are fundamentally differ- 
ent. In their view : 

" Appetite is related to previous sensations of the taste and 
smell of food ; it has therefore, as Pawlow has shown, important 
psychic elements. It may exist separate from hunger, as, for 
example, when we eat delectable dainties merely to please the 



ENZYMES AND DIGESTION 8l 

palate. Sensory associations, delightful or disgusting, deter- 
mine the appetite for any edible substance, and either memory 
or present stimulation can thus arouse desire or dislike for 
food." 

" Hunger, on the other hand, is a dull ache or gnawing sen- 
sation referred to the lower midchest region or epigastrium. 
It is the organism's first strong demand for nutriment, and, not 
satisfied, is Hkely to grow into a highly uncomfortable pang, 
less definitely locaHzed as it becomes more intense. It may 
exist separate from appetite, as, for example, when hunger forces 
the taking of food not only distasteful but even nauseating." 

Hunger is not due merely to emptiness of the stomach. It 
is true that under ordinary conditions hunger is apt to appear 
soon after the last food has passed from the stomach to the in- 
testine, but if the stomach be artificially emptied, the sensation 
of hunger may not be felt until some hours afterward. Nor is 
hunger due to hydrochloric acid secreted into an empty stomach, 
for if the empty stomach of a hungry person be washed out, but 
little if any acid is found. 

The explanation of hunger, advanced by Cannon and Wash- 
burn, is that it is due to the muscular contractions of the walls 
of the empty stomach. 

In order to learn whether direct proof of this might be secured experi- 
mentally in man, one of the investigators accustomed himself to swallowing 
a small soft rubber balloon attached to the end of a rubber tube by means 
Qf which it could be withdrawn when desired. The tube and bulb were 
habitually carried thus in the esophagus and stomach for two or three 
hours at a time until the experience ceased to have any disturbing effect. 
Experiments were then made in which the balloon, thus held in the stomach, 
was partially inflated with air and connected with a manometer and record- 
ing apparatus by means of which any pressure exerted upon the balloon was 
recorded automatically. In the actual experiments, the subject sat at rest 
with his hand on a key which he pressed whenever he experienced the sensa- 
tion of hunger. This key was connected with a recording device which, 
like the apparatus recording the muscular contractions of the stomach upon 
the rubber balloon, was out of sight of the subject. 

G 



82 CHEMISTRY OF FOOD AND NUTRITION 

Before hunger was experienced the recording apparatus revealed no evi- 
dence of muscular activity in the stomach. The records of hunger "pangs" 
and of muscular contractions of the stomach were always approximately 
simultaneous, that is, when the subject of the experiment felt hungry, power- 
ful contractions of the stomach were always being registered. The con- 
tractions were about 30 seconds in duration, with pauses of 30 to 90 seconds 
between. It was found in almost every case that the contraction reached 
its greatest intensity just before the record of the hunger sensation began, 
and that the feeling of hunger disappeared when the contraction ceased 
although no food or drink had been taken. Cannon considers the evidence 
conclusive that hunger is caused by the contractions, and not vice versa, 
as Boldireff had thought. Other observations in the course of Cannon's 
experiments showed that the lower end of the esophagus also contracts 
periodically in hunger, an explanation of the fact that sensations of hunger 
may be felt in cases where the stomach has been removed. Furthermore 
Cannon considers that vague sensations of hunger may also originate from 
muscular contractions in the intestine. 

What causes the stomach contractions which give the sen- 
sation of hunger has not been determined. They do not seem 
to be directly related to bodily need. That they usually begin 
at or soon after the accustomed meal hour may be taken not 
only as evidence that habit plays an important role, but also 
as an indication of the desirability of eating at regular times ; 
for in view of the importance of the muscular tone of the stomach 
walls, these observations seem to justify the view that the strong 
muscular contraction of the empty stomach may be regarded 
as an indication that the condition which causes the first sen- 
sation of hunger is that in which the stomach is in the best state 
of readiness to receive the food. There is also direct experi- 
mental evidence that the stomach digests more expeditiously 
the food which is " eaten with hunger " (Hudek and Stigler, 
cited by Carlson). The description of the digestive process 
which follows presupposes that the food is eaten under favor- 
able conditions and received by a digestive tract which has been 
permitted to form good and regular habits. 

The eating of food induces a flow of saUva from great num- 



ENZYMES AND DIGESTION 83 

bers of minute glands In the lining membrane of the mouth 
and from the three pairs of large salivary glands. That saliva 
is secreted in response to psychic as well as chemical stimulation 
is shown by the fact that actual contact with the food is not 
necessary, since secretion may be started by the sight or odor 
or even the thought of food. Mixed human saliva has usually 
a faintly alkaline reaction and always contains ptyalin (salivary 
amylase), although its amylolytic power appears to vary con- 
siderably with individuals and with the same individual at dif- 
ferent times of the day. As the food comes in contact with 
saUva, the digestion of starch and dextrin under the influence of 
the ptyaUn begins at once ; but as mastication is an entirely 
voluntary act, the thoroughness with which the food becomes 
mixed with saliva is subject to wide variations. 

Usually the food stays too short a time in the mouth for the 
starch to be acted upon there to any great extent, and until 
recently it was supposed that salivary digestion must cease 
almost as soon as the food reaches the stomach, since the ac- 
tivity of ptyalin is quickly checked by even small amounts of 
free hydrochloric acid. It was supposed that the food mass 
must soon be mixed with the gastric juice under the influence 
of the " churning " of the stomach contents by the muscular 
contraction of the stomach walls, which was so interestingly 
described by Dr. Beaumont in the account of his classical re- 
searches already referred to (pages 70-7 1 ) . From the nature of the 
case Dr. Beaumont's observations were made entirely at one point 
in the stomach. Here he found during digestion a vigorous mus- 
cular churning and mixing of the food mass with the gastric juice. 
For a long time this was supposed to represent the state of the 
entire stomach contents. This view has now been abandoned as 
the result of a number of recent investigations, among which 
those of Cannon and of Griitzner are of especial interest. 

When a small amount of an inert metallic compound such as 
bismuth subnitrate is mixed with the food, it becomes possible 



84 



CHEMISTRY OF FOOD AND NUTRITION 



to photograph the food-mass within the body by means of the 
Roentgen rays. By the use of this method Cannon has carried 
out an extended series of observations upon the movements of 
the stomach and intestines during digestion/ upon the results 
of which the statements concerning the mechanism of digestion 
in this chapter are chiefly based. 

Cannon's observations, confirmed by those of other investi- 
gators, show that the vigorous muscular movements described 

by Beaumont, and which gen- 
erally begin 20 to 30 minutes 
after the beginning of a meal, 
occur only in the middle and 
posterior, or pyloric, portion of 
the stomach, while the anterior 
portion, or fundus, which serves 
as a reservoir for the greater 
portion of the food, is not ac- 
tively concerned in these move- 
ments and does not rapidly mix 
its contents with the gastric 
juice. 

That there is no general circu- 
lation and mixing of the entire 
stomach contents during or immediately following a meal is 
further shown by the experiments of Griitzner, who fed rats 
with foods of different colors and on killing the animals and 
examining the stomach contents found that the portions which 
had been eaten successively were arranged in definite strata. 
The food which had been first eaten lay next to the walls of the 
stomach and filled the pyloric region, while the succeeding por- 
tions were arranged regularly in the interior in a concentric 
fashion (Fig. 5). In describing this result Howell says: " Such 




Fig. 5. — Section of frozen stomach 
of rat during digestion to show the 
stratification of food given at differ- 
ent times. {Griitzner.) The food 
was given iri three portions and 
colored differently. Reproduced from 
Howell's Textbook of Physiology, by 
permission of the W. B. Saunders Co. 



1 These and other investigations are fully discussed in Cannon's Mechanical 
Factors in Digestion. See also Carlson's Control oj Uiinger in Health and Disease. 



ENZYMES AND DIGESTION 85 

an arrangement of the food is more readily understood when 
one recalls that the stomach has never any empty space within ; 
its cavity is only as large as its contents, so that the first portion 
of food eaten entirely fills it, and successive portions find the 
wall layer occupied and are therefore received into the interior." 

The character of the gastric juice secreted in different parts 
of the stomach varies considerably, especially as regards its 
acidity. In the middle region the secretion is rich in acid, 
while both in the cardiac region and at the extreme pyloric end, 
the " border cells " or " cover cells " (from which the secretion 
of the acid appears to take place) are few in number or entirely 
lacking, and the juice secreted in these regions may be neutral 
or, according to Howell, even slightly alkaline. 

The nature and extent of the muscular movements also vary 
greatly in the different regions of the stomach. The peristaltic 
waves of muscular constriction which bring about the thorough 
mixing of the food with the gastric juice begin in the middle 
region and travel toward the pylorus. Over the pyloric part 
of the stomach when food is present constriction waves are 
continually coursing toward the pylorus. The food in this region 
is first pushed forward by the running wave and then by pres- 
sure of the stomach wall is returned through the ring of con- 
striction. Thus the food in this portion of the stomach is 
thoroughly mixed with the gastric juice and is forced by an 
oscillating progress toward the pylorus. 

The food in the cardiac end of the stomach is not moved by 
peristalsis, and so comes only slowly into contact with the 
gastric juice ; and since the juice secreted here contains Uttle 
if any free acid, a large part of the food mass remains for some 
time (variously estimated at from 30 minutes to 2 hours or 
more) in approximately the same neutral or faintly alkaUne 
condition in which it was swallowed, and saUvary digestion 
continues in this part of the stomach without interruption. 
Thus, if the food has been thoroughly chewed and well mixed 



86 CHE^IISTRV OF FOOD AND NUTRITION 

with saliva before swallowing, much if nol most of its starch 
may be converted into dextrin and maltose in the cardiac region 
of the stomach before the activity of the ptyaHn is stopped by 
contact with the acid of the gastric juice. 

The fundus, however, is not entirely inactive, but acts as a 
sort of elastic pouch which is distended by and slowly con- 
tracts upon the food mass, thus gradually tending to move the 
posterior portions and particularly the more fluid portion into 
the pyloric region. As digestion proceeds, the pylorus opens 
more frequently and the stomach tends to empty itself more 
and more freely, until finally the pylorus may open to allow 
the passage of particles which have not been acted upon by 
the gastric juice. Whether the stomach will thus completely 
empty itself of one meal before the eating of the next will de- 
pend of course upon the length of the interval and the amount 
and character of the food composing the meal. Small test 
meals may disappear in from i to 4 hours, but meals approxi- 
mating one third of the day's food may not disappear entirely 
from the stomach during 6 or 7 hours. 

In stud^dng the passage of food from the stomach into the in- 
testine. Cannon found that the pylorus does not open at the 
approach of each wave of constriction which passes over this 
part of the stomach, but only at irregular intervals. When the 
observations made by means of the Roentgen rays were sup- 
plemented by chemical examinations of stomach and intestinal 
contents removed at different stages, it appeared that the 
presence of free acid in the pyloric part of the stomach causes 
the pylorus to open, and its presence in the small intestine 
causes the pylorus to close. Thus it would appear that under 
normal conditions it is only when the protein of the food has 
become more or less completely saturated with hydrochloric 
acid and some of the latter remains in the free state, that the 
food is allowed to pass into the intestine. 

Ordinarily, when each is fed separately, protein food stays 



ENZYIMES AND DIGESTION 87 

longer in the stomach than carbohydrate, fat longer than pro- 
tein, and mixtures of fat and protein leave the stomach more 
slowly than either alone. This is probably because fat tends to 
retard both the motiUty of the stomach and the secretion of the 
acid gastric juice. In general the softer or more fluid the fat 
the more rapidly it will leave the stomach ; also emulsified fats 
tend to pass on more promptly than fat of the same kind taken 
in larger masses. 

The difference noted between protein and carbohydrate is 
doubtless due to the fact that combination of the acid of the 
gastric juice with the protein of the food delays the appearance 
of free acid at the pylorus ; for when protein food was acidulated 
before feeding and carbohydrate food was made alkaline, the 
protein was found to leave the stomach more rapidly than the 
carbohydrate. That the passage of food from stomach to 
intestine is governed mainly by the degree of acidity reached 
in the pyloric part of the stomach is of interest in view of the 
importance to the organism of the action of the acidity of the 
gastric juice in effecting a partial disinfection of the food. It 
has been found that when through any cause the hydrochloric 
acid of the gastric juice is abnormally decreased, the numbers 
of bacteria in the stomach contents may increase greatly. It 
will be seen also that the acidity of the chyme as it passes 
the pylorus has an important influence upon the secretion of 
the pancreatic juice. 

The most important characteristics of gastric juice are the 
presence of free hj^drochloric acid and of pepsin. While other 
acids may be found in stomach contents, the acidity of gastric 
juice appears to be due entirely to hydrochloric acid. Normal 
human gastric juice has been found by different observers to 
contain about 0.2 to 0.4 per cent of free hydrochloric acid.* 

♦According to Carlson, "hunger juice" and "appetite juice" in man contain 
respectively 0.25 per cent and 0.40 per cent of free hydrochloric acid — averages of 
hundreds of obser\'ations upon a healthy man having a gastric fistula. 



88 CHEMISTRY OF FOOD AND NUTRITION 

The stimuli which bring about secretion of gastric juice are 
both psychical and chemical. 

Psychical stimulation results from the sensations of eating and may also 
be due to the sight and odor of food. The psychical secretion is studied 
chiefly by means of the "fictitious feeding" ("sham feeding") experiments 
in which food is given to dogs which have been prepared with esophageal 
openings through which the swallowed food escapes without entering the 
stomach. When such a dog is fed with meat, for example, there is a con- 
siderable secretion of gastric juice in spite of the fact that no food reaches 
the stomach. Such a flow of gastric juice is due to impulses received through 
the nervous system and specifically through the vagus nerve, for fictitious 
feeding has been found to cause a flow of gastric juice when the vagi are 
intact, but not after they have been cut. Secretion produced in this way 
reflexly as the result of the sensation of taste, odor, etc., is called by Pawlow 
a "psychic secretion" or "appetite juice." When the secretion is once 
started, even if no food enters the stomach, the flow of juice maj' continue 
for some time after the stimulus has ceased. 

On the other hand, the normal secretion of gastric juice may be checked 
by unpleasant feelings such as fear, anger, or pain. This has been repeatedly 
observed with frightened or angry animals. Hornborg reports a similar 
observation upon a small boy. Food was shown but withheld, and the child 
became vexed and distressed, whereupon no gastric juice was secreted. After 
he was calmed, and given the food, it was some time before secretion began. 
Cannon infers, furthermore, that there is a "psychic tone" or "psychic 
contraction" of the gastro-intestinal muscles, analogous to the psychic 
secretion. In the same fashion that secretion may be checked, so also the 
movements of the stomach, bringing about the mixing of food with gastric 
juice and insuring its passage on into the duodenum, may be stopped during 
excitement or pain. This fact has been observed many times in experi- 
ments w^ith various animals, as well as in the case of human beings. 

If psychic secretion is normally excited, it insures the prompt 
beginning of gastric digestion. Stimulations arising within the 
stomach itself supplement the psychic influences and provide 
for the continued secretion of the gastric juice long after the 
mental effects of a meal have disappeared. This second stimu- 
lation is chemical and depends upon the production in the py- 
loric mucous membrane of a specific substance, or hormone, 
which acts as a chemical messenger to all parts of the stomach, 



ENZYMES AND DIGESTION 89 

being absorbed into the blood and thence exciting the activity 
of the various secreting cells of the gastric glands (Starling). 
Meat extracts, soups, etc., are particularly active in exciting 
the secretion which depends upon chemical stimulation; milk 
causes less secretion ; white of egg is said to have no effect. 

Under normal conditions, the amount of nutritive material 
absorbed from the stomach is insignificant as compared with 
the amount absorbed from the intestine. Nearly all the food 
eaten is passed from the stomach into the intestine in the form 
of chyme, having been more or less perfectly liquefied and acid- 
ulated by its thorough mixing with the gastric juice in the middle 
and pyloric regions of the stomach. 

The stomach therefore has several functions. It serves (i) 
as a storage reservoir receiving food in relatively large quanti- 
ties, say three times a day, and passing it on to the intestine in 
small portions at frequent intervals, (2) as a place for the con- 
tinuation of the salivary digestion of starch, and (3) for the 
beginning of the digestion of proteins and perhaps fats, and 
finally (4) as a disinfecting station by virtue of the germicidal 
action of the hydrochloric acid of the gastric juice. 

Intestinal Digestion 

Digestion in the small intestine. — When the pylorus opens, 
food, now reduced to liquid chyme, is projected into the upper 
part of the small intestine, where it usually lies for some time 
in the curve of the duodenum, until several additions have 
been made to it from the stomach. While the food rests here 
the bile and pancreatic juice are poured out upon it, and here 
also, as well as in other parts of the small intestine, a certain 
amount of intestinal digestive juice (" succus entericus ") 
is secreted by the glands of the Hning membrane and mixed 
with the intestinal contents. While for purposes of descrip- 
tion the pancreatic and intestinal juices and the bile may be 



go CHEMISTRY OF FOOD AND NUTRITION 

discussed separately, it is to be remembered that in normal 
digestion they always act together. Cannon's observations 
showed that after a certain amount of food and digestive 
juices has accumulated as just described in the first loop of 
the small intestine, the mass all at once becomes segmented 
by constrictions of the intestinal walls, and the segmentation 
is repeated rhythmically for several minutes, so that the in- 
dividual portions are subjected to relatively extensive and 
energetic to-and-fro movement, which is doubtless very im- 
portant in facilitating the emulsification of fat. Other effects 
of the muscular constrictions which cause the segmentation are 
(i) a further mixing of food and digestive juices, (2) the bring- 
ing of the digested food into contact with the absorbing mem- 
brane, (3) the emptying of the venous and lymphatic radicles 
in the membrane, the material which they have absorbed being 
forced into the veins and lymph vessels by the compression of 
the intestinal wall. After a varying length of time the seg- 
mentation ceases and the small segments are carried forward 
individually by the peristaltic movement, or join and move on 
as a single body. 

The fluid food mass which the stomach pours into the duo- 
denum contains a small amount of free hydrochloric acid be- 
sides a larger amount combined with protein and sometimes or- 
ganic acids from the food as eaten, or from bacterial fermentation 
of carbohydrates in the stomach. The pylorus having closed, 
the alkalinity of the bile, the pancreatic juice, and the intestinal 
juice combine to neutralize the acids present. 

In man the main duct of the pancreas and the bile duct unite 
and empty into the small intestine about 8 to 10 cm. (3 to 4 
inches) below the pylorus. The pancreatic juice is a clear liquid 
having an alkalinity probably equivalent to a 0.5 per cent 
solution of sodium carbonate and containing three important 
enzymes or their zymogens — trypsin, amylopsin (amylase), 
and steapsin or lipase. 



ENZYMES AND DIGESTION 91 

The outflow of the pancreatic juice begins at once when any 
of the acid stomach contents passes through the pylorus, and 
has been shown by BayHss and StarUng to be due to a definite 
chemical substance, secretin, a typical hormone produced as 
the result of the action of the acid upon some constituent of 
the intestinal mucous membrane, which is absorbed and carried 
by the blood to the pancreas and there stimulates the flow of 
pancreatic juice. 

Human bile, which, as already stated, enters the intestine 
through the same duct with the pancreatic juice, is a slightly 
alkaline solution containing, in addition to water and salts, 
bile pigments, bile acids (as salts), cholesterin, lecithin, and a 
pecuHar protein derived from the mucous membrane of the 
bile ducts and gall bladder. The presence of the bile in the 
intestinal contents greatly increases the solubility of the fatty 
acids, while at the same time it diminishes the surface tension 
between watery and oily fluids. Bile may also accelerate the 
action of pancreatic lipase in a more direct way. Thus bile 
aids both the digestion and the absorption of fats. The bile 
acids are themselves absorbed to a considerable extent and 
again secreted by the liver. The secretion of bile by the liver, 
although variable in amount, is continuous. Its ejection from 
the gall bladder into the intestine occurs, however, only during 
digestion, and appears to be excited by the passage of chyme 
through the pylorus, and to run parallel to the outpouring of 
the pancreatic juice. According to Starling, the rapid flow of 
bile during intestinal digestion is due not only to the pouring 
out of what was previously stored in the gall bladder, but also 
to an increased rate of secretion to which the liver is stimulated 
by the same chemical mechanism which stimulates the flow 
of pancreatic juice. 

The intestinal juice is a distinctly alkaline liquid secreted by 
the tubular glands (crypts of Lieberkiihn) with which the small 
intestine is lined. It contains at least five enzymes : entero- 



92 CHEMISTRY OF FOOD AND NUTRITION 

kinase, by the action of which trypsinogen is converted into 
trypsin , erepsin, which produces further cleavage of the pro- 
teoses and peptones; and the three enzymes, sucrase (or in- 
vertase), maltase, and lactase, which hydrolyze respectively the 
three disaccharides, sucrose, maltose, and lactose. The secre- 
tion of intestinal juice is probably stimulated by secretin, and 
possibly also by another hormone whose production is de- 
pendent upon the presence of pancreatic juice. 

Careful observations on the reaction of the contents of the 
small intestine were made by Moore and Bergin in 1897.* 
Samples taken through a fistula immediately above the ileo- 
caecal valve were always alkaline to methyl-orange, lacmoid, 
and litmus, but acid to phenolphthalein. Hence neither 
hydrochloric acid, nor any appreciable amount of the stronger 
organic acids such as acetic, butyric, or lactic, could have been 
present in the free state. The acid reaction shown by phe- 
nolphthalein was probably due either to traces of organic acids, 
or possibly to dissolved carbonic acid, or to acid-protein com- 
pounds not yet completely digested and absorbed. It seems 
probable that this fairly represents the condition as to reaction 
which exists throughout the greater part of the small intestine. 
Under such conditions all three classes of foodstuffs would be 
readily attacked by the digestive enzymes present, and brought 
into condition for absorption — the carbohydrates as mono- 
saccharide; the fats as fatty acid and glycerol; the proteins 
(chiefly at least) as amino acids. 

The rate of passage of different foodstuffs through the small 
intestine has been studied by Cannon with the aid of the Roent- 
gen rays, according to the general method already described. 
Fat, carbohydrate, and protein foods, uniform in consistency 
and in amount (25 cc), were fed to cats which had been fasted 

* Very recently the subject has been reinvestigated by Long and Fenger, using 
modern methods for the actual measurement of hydrogen ion concentration. See 
Journal oj the American Chemical Society, June, 1917. 



ENZYMES AND DIGESTION 93 

for 24 hours. At regular intervals for 7 hours after feeding, 
the shadows of the stomach and intestinal contents were ob- 
served by means of the Roentgen rays. 

The process of rhythmic segmentation above described was 
seen with all three kinds of foodstuffs, and the frequency of its 
occurrence corresponded roughly to the amount of food present 
in the intestine. 

Absorption takes place very readily in the small intestine — ■ 
more readily and completely than can be explained by the purely 
mechanical laws of diffusion. On this account the process is 
sometimes called " resorption " to distinguish it from passive 
absorption such as takes place by diffusion through non-living 
membrane. 

Observations have been made upon a patient having a fistula 
at the end of the small intestine. In this case it was found 
that 85 per cent of the protein matter of the food was absorbed 
before this point was reached, and the absorption of the other 
foodstuffs is probably equally complete. For this patient 
the food began to pass the ileocaecal valve in from 2 to 5! hours 
after eating, but the time required from the eating of the food 
until the last portions had passed into the large intestine was 
9 to 23 hours. 

Digestion in the large intestine. — We have seen that in 
the small intestine the conditions are very favorable both for 
digestion and for absorption, and that very much the greater 
part of the available nutrients has been absorbed before the 
food mass reaches the ileocaecal valve. Hertz has observed, 
however, that often the ileum is still full at the end of four or 
five hours after the last trace of chyme has left the stomach. 
Consequently there may be an accumulation of incompletely 
digested food and active digestive enzymes in the last few inches 
of the ileum, where it remains and undergoes digestion for 
perhaps a longer period than in the stomach. During all this 
time there is active segmentation, but very little peristalsis. 



94 CHEMISTRY OF FOOD AND NUTRITION 

Beginning at infrequent intervals some time after the chyme 
first reaches it, the ileocaecal valve relaxes each time a peri- 
staltic wave passes along the last few inches of the ileum. Can- 
non finds that the ileocaecal valve is physiologically " com- 
petent " for food which passes through it normally from the 
small intestine. This means that the food which has reached 
the large intestine in the natural way is ordinarily never forced 
back into the small intestine again. This is important because 
in the anterior portion of the large intestine the waves which 
appear most frequently are those of antiperistalsis — i.e. tend 
to force the food back toward the small intestine. Since the 
ileocaecal valve prevents the food passing back, these antiperi- 
staltic waves result in thoroughly churning the food in this 
part of the large intestine and constantly bringing fresh por- 
tions in c!ontact with the intestinal wall so that the conditions 
here are quite favorable for absorption. IVIoreover, the walls 
of the large intestine furnish an alkaline secretion which further 
aids the completion of the digestive changes already begun. 
So far as known the large intestine secretes no digestive enzyme 
of its own. 

With the passage of material from the ileum into the caecum, 
the caecum and ascending colon become gradually filled. Recent 
observations show that this passive filling takes place very slowly 
except during and immediately after meals (Hertz). The 
material remains in the large intestine for a comparatively long 
time (generally about a day, often longer) ; for the peristaltic 
movements which carry the material onward, while stronger 
than the waves of antiperistalsis, are of less frequent occur- 
rence, at least in the first part of the large intestine. During 
this time there is a marked absorption of water, along with 
the remaining products of digestion. The residual material 
gradually becomes more solid and takes on the character 
of feces. 



ENZYMES AND DIGESTION 95 

Bacterial Action in the Digestive Tract 

The digestive tract of an infant contains no bacteria at birth, 
but usually some gain access during the first day of life. In the 
average adult it is estimated that each day's food in its passage 
through the digestive tract is subjected to the action of over 
one hundred bilHon bacteria, chiefly in the large intestine. 

Since bacteria are regularly present in the digestive tract in 
such large numbers, it has been questioned whether they may 
not perform some essential function in connection with the nor- 
mal processes of digestion. Experiments to demonstrate whether 
animals are independent of such bacteria are beset with many 
difficulties. Nuttall and Thierfelder kept sterile for several 
days the digestive tracts of young guinea pigs delivered by 
Caesarean section and fed upon thoroughly sterilized food, and 
as the animals thus treated lived and gained in weight, the 
experimenters concluded that intestinal bacteria are not es- 
sential to normal nutrition. This view has recently received 
strong support from the observations of Levin, who examined 
the intestinal contents of Arctic animals in Spitzenberg. The 
digestive tracts of white bears, seals, reindeer, eider ducks, and 
penguin were found to be in most cases free from bacteria, 
sho\ving that the latter are not essential to the normal processes 
of digestion and nutrition. Kendall, however, in citing the evi- 
dence presented by Levin, points out that Arctic mammals, 
as soon as they are brought to temperate regions, rapidly ac- 
quire intestinal bacteria which do not seem to interfere with 
the well-being of the host. 

Furthermore Schottelius claims that the conclusions of Nut- 
tall and Thierfelder are not justified since their experiments did 
not cover a long enough period. He himself experimented with 
chickens from bacteria-free eggs. One group kept in an 
absolutely bacteria-free environment and fed on sterile food, did 
well for ten days, but thereafter developed very slowly. When 



96 CHEMISTRY OF FOOD AND NUTRITION 

they were given " infected " food (containing common bacteria), 
they gained rapidly. Meanwhile a second group which had 
been kept in a sterile environment but had received " infected " 
food from the start, grew normally, as did a third group kept 
throughout under ordinary conditions. From these results 
Schottelius concluded that intestinal flora seem to be necessary 
for the normal development of chickens. Similar observations 
have been made by Madame MetschinikofE using tadpoles, 
and by Moro using turtles. 

Notwithstanding this conflicting evidence, it would seem fair 
to conclude from the observations of Levin that if it were 
possible to exclude absolutely all bacteria from the digestive 
tract, the well-being of the body would be in no wise im- 
paired ; yet under such conditions as ordinarily exist, the 
bacteria which usually predominate in the digestive tract of 
the healthy man probably render an important service in 
helping to protect the body against occasional invasions of 
obnoxious species. 

According to Herter, a few species, such as B. lactis aerogenes, 
B. coli, B. bifidus, have adapted themselves so well to the con- 
ditions existing in the human digestive tract that they are 
ordinarily not harmful to the host unless present in abnormally 
large numbers, and being able to hold their own against new- 
comers they may act beneficially in giving rise to conditions 
which check the development of other types of organisms, 
capable of doing injury, which under ordinary conditions man 
can hardly prevent from occasionally gaining ingress through 
food or drink. 

" The presence in the colon of immense numbers of obligate 
micro-organisms of the B. coli type may be an important de- 
fense of the organism in the sense that they hinder the develop- 
ment of that putrefactive decomposition which, if prolonged, 
is so injurious to the organism as a whole. We have in this 
adaptation the most rational explanation of the meaning of 



ENZYMES AND DIGESTION 97 

the myriads of colon bacilli that inhabit the large intestine. 
This view is not inconsistent with the conception that under 
some conditions the colon bacilli multiply to such an extent as 
to prove harmful through the part they take in promoting 
fermentation and putrefaction." 

Proteolytic enzymes formed by intestinal bacteria may 
assist in the digestion of food, and it is conceivable that bac- 
teria may synthesize proteins or amino acids which may then 
be absorbed by the host, but the recent experiments of Osborne 
and Mendel seem to show that this cannot be an important 
factor in protein metabolism. 

If for our present purpose we consider only the bacteria which 
are prominent in producing decomposition of foodstuffs in the 
digestive tract, and these only with reference to this one prop- 
erty, we may regard as the three main types: (t) the bacteria 
of fermentation, such for example as the lactic acid bacteria ; 
(2) the putrefactive bacteria, such as the anaerobic B. aerogenes 
capsulatus (B. welchii); (3) bacteria of the B. coll type, showing 
some of the characters of both the fermentative and putre- 
factive organisms, but tending in general to antagonize the 
putrefactive anaerobes. 

Among cases of excessive bacterial decomposition in the 
digestive tract the fermentation of carbohydrates with pro- 
duction of organic acids (and possibly also alcohol) is most 
likely to occur in the stomach, while the putrefaction of pro- 
teins occurs mainly in the large intestine. While it is true 
that in general the products of fermentation tend to restrict 
putrefaction, yet, since the two processes take place for the most 
part at such widely separated points of the digestive tract, 
there may be excessive fermentation and excessive putrefac- 
tion in the same individual at the same time. Among the con- 
ditions which favor excessive fermentation are : diminished tone 
and motihty of the stomach, dilation, diminution or absence of 
free hydrochloric acid in the gastric juice, and excessive use of 

H 



98 CHEMISTRY OF FOOD AND NUTRITION 

carbohydrate food — especially sucrose and glucose, which 
are more susceptible to fermentation in the stomach than are 
lactose, maltose and starch. 

In the normal human stomach the conditions are quite 
unfavorable for the development of anaerobic putrefactive 
bacteria, not only because of the presence of air, but also because 
of the action of the gastric juice ; and favorable conditions are 
not found in the anterior portion of the small intestine. In 
the lower third of the small intestine the numbers of bacteria 
increase and among them sometimes putrefactive forms. In 
the large intestine the conditions are much more favorable 
for the anaerobic putrefactive bacteria, and these may produce 
marked decomposition in any protein still remaining unabsorbed. 
In general the greater the amount of digestible but undigested 
or unabsorbed protein and the longer the material stays in the 
large intestine, the greater the amount of putrefactive de- 
composition. Not infrequently excessive fermentation in the 
stomach causes local sensitiveness which results in the taking 
of less bulky food (or such as has less indigestible residue), 
which in turn tends to stagnate in the intestine and thus render 
the conditions more favorable for intestinal putrefaction. Ac- 
cording to Herter there sometimes results from the eating of 
large quantities of meat and sugar a type of fermentation in 
which oxaHc acid is produced and which must therefore be 
highly injurious; but ordinarily the products of fermentation 
are only irritating, while putrefaction gives rise to products 
which are more distinctly toxic. These include indol, skatol, 
phenol, and cresol, which are for the most part absorbed into 
the system and finally excreted in combination with sulphuric 
acid as " ethereal " or " conjugated " sulphates. Of these the 
best-known is potassium indoxyl sulphate, commonly called 
" indican." The amounts of conjugated sulphates and of in- 
dican in the urine are valuable indications of the intensity of 
the putrefactive process in the intestine. 



ENZYMES AND DIGESTION 



99 



CoeflBcients of Digestibility of Food 

The fecal matter passed per day varies considerably in health, 
but, on an ordinary mixed diet of digestible food materials, is 
usually between loo and 200 grams of moist substance contain- 
ing 25 to 50 grams of solids. The feces contain any indigestible 
substances swallowed with the food and any undigested resi- 
dues of true food material ; but ordinarily they appear to be 
largely composed of residues of the digestive juices, together 
with certain substances which have been formed in metabohsm 
and excreted by way of the intestine, and bacteria, Uving and 
dead. 

Prausnitz studied the feces of several persons placed alter- 
nately on meat and on rice diets and found that, although the 
solids of the meat were about ten times as rich in nitrogen as 
the solids of the rice, the two diets yielded feces whose soHds 
were of practically the same composition. Some of the data of 
these experiments are shown in the table. 

Composition of Feces from Different Diets (Prausnitz) 



Person 


Principal 

FOOD 


Nitrogen in 
dry feces per cent 


Ether Extract 
in dry feces 

per CENT 


Ash in dry 

FECES per CENT 


H. ... 
H. ... 
M. ... 
M. ... 
W. P. . . 
W. P. . . 


Rice 

Meat 

Rice 

Meat 

Rice 

Meat 


8.83 
8.75 
8.37 
9.16 

8.59 
8.48 


12.43 
15.96 
18.23 
16.04 
15.89 
17-52 


15-37 
14.74 
11.05 

12.22 

12.58 
13-13 



In view of such results Prausnitz considers that " normal " 
feces have essentially the same composition irrespective of the 
food, the quantity of food residues in such " normal " feces 
being negligible. From this point of view the feces show not 
so much the extent to which the food has been absorbed as 



lOO CHEMISTRY OF FOOD AND NUTRITION 

whether it is a large or a small feces-former. On the other 
hand, so far as the nitrogen compounds of the feces are con- 
cerned, it is probably true, as generally assumed, that they 
represent material either lost or expended in the work of di- 
gestion, and therefore that the nitrogen of the feces is to be de- 
ducted from that of the food in estimating the amount avail- 
able for actual tissue metabolism. This, however, is by no 
means equally true of the ash constituents, many of which after 
being metabolized in the body are eliminated mainly by way of 
the intestine rather than through the kidneys. 

On a Uberal diet consisting entirely of non-nitrogenous food 
the amount of nitrogen in the feces was 0.5 to 0.9 gram per 
day, which is more than is sometimes found in feces from food 
furnishing enough protein to meet all the needs of the body. 
Thus the expenditure of nitrogenous material in the digestion 
of fats and carbohydrates may be larger than in the digestion 
of protein food. 

The feces always contain fat (or at least substances soluble 
in ether) as well as protein. Fasting men have ehminated 
0.57 to 1.3 grams of " fat " per day ; and when the diet is very 
poor in fat, the feces may contain as much as was contained 
in the food. As the fat content of the food rises, the actual 
amounts in the feces increase, but the relative amounts de- 
crease, so that up to a certain point the apparent percentage 
utiHzation of the fat becomes higher. The limit to the amount 
of fat which can be thus well digested varies with the individual 
and with the form in which the fat is given. Quantities up to 
200 grams per day have been absorbed to within 2 to 3 per cent 
when given in the form of milk, cheese, or butter. 

In addition to protein and fat the feces always contain various 
other forms of organic matter which in the routine proximate 
analyses usually made in connection with feeding experiments 
are collectively reported as " carbohydrates determined by 
difference." 



ENZYMES AND DIGESTION 



lOI 



With these facts in mind one may make use of the coefficients 
of digestibiHty without being misled by them. These co- 
efficients show the relation between the constituents of the 
food consumed and the corresponding constituents of the feces. 
Thus if the feces from a given diet contain 5 per cent as much 
protein as was contained in the food, this proportion is as- 
sumed to have been lost or expended in digestion, and the co- 
efficient of digestibility of the protein of the diet is stated to 
be 95 per cent. While as just shown this assumption is not 
entirely correct, yet it is approximately true of the organic 
nutriments that the difference between the amounts in the 
food and in the feces represents what is available to the tissues 
of the body, and thus these coefficients serve a useful purpose 
in the computation of the nutritive values of foods. 

From the results of hundreds of digestion experiments At- 
water computed the coefficients of digestibility of the organic 
nutrients of the main groups of food materials, when used by 
man as part of a mixed diet, to be as follows : — 

Average Coefficients of Digestibility of Foods when Used in Mixed 
Diet (Atwater) 





Protein 


Fat 


Carbohydrates 




PER CENT 


PER CENT 


PER CENT 


Animal foods 


97 


95 


98 


Cereals and breadstuffs 


85 


90 


98 


Dried legumes .... 


78 


90 


97 


Vegetables 


83 


90 


95 


Fruits 


85 


90 


90 


Total food of average mixed 








diet 


92 


95 


98 



In some cases these figures are higher than have been re- 
ported for similar foods by other observers, the differences 
being due mainly to the fact (not formerly recognized) that a 
food may be more perfectly utiUzed when fed as part of a 



I02 CHEMISTRY OF FOOD AND XUTRFnON 

simple mixed diet than when fed alone. Milk is an example 
of such a food, and has when consumed as part of a mixed diet 
a much higher coefficient of digestibility than is often assigned 
to it on the basis of earlier experiments. 

It will be seen that the coefficients differ less for the different 
types of food than might be expected from popular impressions 
of " digestibility " and " indigestibility." It is also note- 
worthy that the coefficients of digestibility are less influenced 
by the conditions under which the food is eaten and vary less 
with individuals than is generally supposed. In explanation 
of this it may be noted that general impressions of digestibility 
relate mainly to ease of digestion and particularly to ease and 
rapidity of gastric digestion, and that there is Httle direct 
relation between the ease with which a food is digested in the 
stomach and the extent to which it is ultimately digested in 
its passage through the entire digestive tract. Substances 
which are resistant to gastric digestion will tend to remain long 
in the stomach and will probably excite a greater flow of gastric 
juice. Thus a greater amount of acid chyme will enter the 
duodenum, and this will result in the secretion of a greater 
amount of pancreatic juice also. 

Similarly an increase in the amount of food eaten may have 
little effect upon the coefficient of digestibility of the foodstuffs. 
In a series of experiments by the writer it was found that the 
doubling of a small diet decreased the coefficient of digestibility 
by less than i per cent. Snyder reports that as between medium 
and large amounts of oatmeal and milk, the protein was 7 per 
cent and the fat 6 per cent more completely absorbed in the 
case of the medium ration. 

REFERENCES 

Bayliss. Principles of General Physiology. 
Bayliss. The Nature of Enzyme Action. 
Cannon. The Mechanical Factors of Digestion. 



ENZYMES AND DIGESTION 103 

Cannon and Washburn. An Explanation of Hunger. American Journal 

of Physiology, Vol. 29, page 441 (1911). 
Carlson. The Control of Hunger in Health and Disease. 
Effront. Les Catalyseurs Biochemique. 
EULER. General Chemistry of the Enzymes. 
Falk and Sigiura. The Esterase and Lipase of Castor Beans. Journal 

of the American Chemical Society, Vol. 37, page 217 (1915). 
Falk. An Experimental Study of Lipolytic Actions. Proceedings of 

National Academy of Science, Vol. i, page 136 (March 1915). Journal 

of Biological Chemistry, Vol. 31, page 97 (191 7). 
Fischer. Physiology of Alimentation. 

Hull and Keeton. The Existence of a Gastric Lipase. Journal of Bio- 
logical Chemistry, Vol. 32, page 127 (191 7). 
Herter. Bacterial Infections of the Digestive Tract. 
Howell. Textbook of Physiology. 
Mathews. Physiological Chemistry, Chapters 8, 9, 10. 
Metchnikoff and Woolman. Studies on Intestinal Putrefaction. An- 

nales de VJnstitute Pasteur, Vol. 27, page 825 (19 12). 
Nelson and Vosburgh. Kinetics of Invertase Action. Journal of the 

American Chemical Society, Vol. 39, page 790 (April 191 7). 
Oppenheimer. Die Fermente. 
Osborne. The Chemical Nature of Diastase. Journal of the American 

Chemical Society, Vol. 17, page 593 (1895). • 
Osborne and Mendel. The Contribution of Bacteria to the Feces. Jour- 
nal of Biological Chemistry, Vol. 18, page 177 (1914). 
Pawlow. The Work of the Digestive Glands. 
Schmidt and Strassburger. Die Faezes des Menschen in normalen und 

krankhaften Zustande. 
Sherman and Gettler. The Forms of Nitrogen in Pancreatic and Malt 

Amylase Preparations. Journal of the American Chemical Society, 

Vol. 35, page 179 (1913)- 
Sherman ant) Schlesinger. Pancreatic Amylase. Ibid., Vol. :i^, page 

1195; Vol. 34, page 1 104; Vol. 37, page 1305 (1911-1915). 
Starling. Recent Advances in the Physiology of Digestion. 
Taylor. Digestion and Metabolism. 
Vernon. Intracellular Enzymes. 



CHAPTER V 

THE FATE OF THE FOODSTUFFS IN METABOLISM 

CARBOHYDRATES 

The carbohydrate of the food, having been converted into 
monosaccharides in the intestine, is taken up by the capillary 
blood vessels of the intestinal wall and passes from them into 
the portal vein. After a meal rich in carbohydrate the blood 
of the portal vein is rich in glucose, sometimes reaching twice 
its normal glucose content ; and may show levulose and galac- 
tose as well. In the blood of the general circulation, however, 
only glucose is found, and this remains small in quantity — 
about one tenth of one per cent — even after a meal rich in 
carbohydrates, so that a considerable part of the carbohydrate 
taken must be stored temporarily in the liver and given up 
gradually to the blood in the form of glucose, thus keeping nearly 
constant the glucose content of the blood of the general cir- 
culation. The carbohydrate thus stored in the liver cells is 
deposited in the form of glycogen, which, after an abundant 
meal, may reach lo per cent of the weight of the liver (or, in 
rare cases, an even higher figure) and may fall to nearly nothing 
when no carbohydrate food has been taken for some time. 
To a less extent the muscles store glycogen in a similar 
way, their glycogen contents varying from traces to about 2 
per cent. 

The fact that the carbohydrate stored in the liver after a 
meal is so largely converted into glucose and passes into the 

104 



THE FATE OF THE FOODSTUFFS IN METABOLISM 1 05 

blood current before the next meal, while the glucose content 
of the blood remains small and nearly constant, indicates that 
the glucose of the blood must be quite rapidly used, and from 
our present standpoint the most important question of the car- 
bohydrate metabolism is the fate of the glucose carried to the 
muscles and other tissues by the blood. 



Oxidation of Carbohydrate 

By comparison of the arterial and venous blood, it is plain 
that in its passage through the muscles the blood becomes 
poorer in glucose and oxygen and richer in carbon dioxide, and 
this change is more marked when the muscle is active than 
when it is at rest. The oxidation of glucose in the muscles is 
in some way dependent upon the pancreas, but the exact func- 
tion of the pancreas in this connection is still obscure. It is 
not to be supposed that the glucose is burned directly to carbon 
dioxide and water. There is much evidence that the glucose 
molecule is broken before oxidation, and in all probability this 
first cleavage yields mainly three-carbon compounds. 

Some lactic acid is always produced by working muscle and 
this has long been regarded as a possible intermediate product 
in the metabolism of glucose.* Lactic acid appears to bear 
important relationships both to carbohydrate metabolism and 
to muscle contraction. The discussion of the significance and 
role of lactic acid cannot be attempted here. It may be said, 
however, that in recent years much experimental evidence has 
accumulated in support of the view that lactic acid is not 
formed directly from glucose, but rather through the inter\en- 
tion of other three-carbon compounds, probably glyceric alde- 
hyde or methyl glyoxal (pyruvic aldehyde) or both. 

* It should perhaps be noted here that lactic acid plays a part not only in the 
metabolism of carbohydrate but of other foodstuffs as well. It may be formed, 
for instance, from glycerol and from certain amino acids. 



Io6 CHEMISTRY OF FOOD AXD NUTRITION 

If we think of the glucose molecule as first breaking into 
three-carbon molecules with a minimum of internal rearrange- 
ment, the most probable primary product would appear to be 
glyceric aldehyde, the formation of which might be represented 
crudely as follows : 

CHoOH • CHOH • CHOj H • CHOH ■ CHOH ■ CHO 

Or, to write the reaction in a more usual form, 
CeHiaOe-^ 2 CH2OH • CHOH • CHO 

Glucose Glyceric aldehyde 

It is also possible that the first product of cleavage of glu- 
cose may be pyruvic aldehyde or methyl glyoxal : 

CeHioOe^ 2 CH3 • CO • CHO + 2H2O 

Glucose Methyl glyoxal 

(Pyruvic aldehyde) 

Both glyceric aldehyde and methyl glyoxal have been shown 
to result from the cleavage of glucose under the influence of 
alkali in vitro and there are doubtless enzymes in the tissues 
which catalyze one or both of these reactions with the result 
that glucose readily undergoes such cleavage as a preliminary 
to oxidation in the body. 

Opinion is at present divided as to whether glyceric aldehyde 
or pyruvic aldehyde (methyl glyoxal) is to be regarded as the 
usual first step in glucose metabohsm. In either case it is prob- 
able that the bulk of the carbohydrate material passes through 
the form of pyruvic aldehyde (methyl glyoxal) on its way to 
oxidation. 

According as we assume the process to go on with or with- 
out the intermediary formation of glyceric aldehyde, the pro- 
duction of lactic acid from glucose in the body may be rep- 
resented in either of the following ways : 

CeHisOe^ CH2OH • CHOH • CHO^ CH3 ■ CO CHO 

Glucose Glyceric aldehyde Pyruvic aldehyde 



THE FATE OF THE FOODSTUFFS IN METABOLISM 1 07 





-^ CH3 ■ CHOH • COOH 




Lactic acid 


or 






CeHioOe -^ CH3 • CO • CHO ^ CH3CHOH • COOH 




Glucose Pyruvic aldehyde Lactic acid 



Each of these reactions has been brought about in the labora- 
tory by heating with alkaU and at the lower alkalinity of the 
body the tissue enzymes are believed to catalyze the same or 
similar changes. Moreover it has been shown that under suit- 
able experimental conditions lactic acid is formed from gly- 
ceric aldehyde and from pyruvic aldehyde by the action of 
surviving liver tissue ; and the further fact that in experimental 
diabetes glucose may be formed from glyceric or pyruvic alde- 
hyde as well as from lactic acid tends also to confirm the belief 
that these aldehydes are intermediary products between glucose 
and lactic acid — both in normal metaboHsm and experimental 
diabetes. Glycerol also when perfused through liver tissue yields 
lactic acid, and since the first product of oxidation of glycerol is 
in all probability glyceric aldehyde, we have here a further reason 
for believing that the latter is a normal precursor of lactic acid. 
There has been no direct demonstration of the presence of 
glyceric aldehyde or of pyruvic aldehyde (methyl glyoxal) in 
the body ; but this is probably due to their unstable or highly 
reactive nature. The view that glyceric aldehyde passes through 
pyruvic aldehyde in being transformed into lactic acid is not 
only probable on stereochemical grounds but is strongly sup- 
ported by much recent evidence indicating that pyruvic 
aldehyde occupies a central position in the intermediary me- 
tabolism. 

Thus far in our study of the catabolism of glucose we have 
considered no oxidative changes but only the cleavages and 
transformations which, from the standpoint of the use of glu- 
cose as fuel, may be regarded as preliminary to oxidation. 
Probably the first oxidation product to be formed in glucose 



Io8 CHEMISTRY OF FOOD AND NUTRITION 

cataboHsm is pyruvic acid, CH3 • CO • COOH. This may be 
formed by the oxidation either of pyruvic aldehyde or of lactic 
acid. The relation of the three substances may be represented 
thus: 

CH3 • CO • CHO i CH3 • CHOH ■ COOH 

Pyruvic aldehyde Lactic acid 

CH3 • CO • COOH 

Pyruvdc acid 

Pyruvic aldehyde and lactic acid are, so to speak, upon the 
same energy plane. Molecule for molecule they are of equal 
fuel value and either is readily convertible into the other. The 
conversion of pyruvic acid into lactic acid or pyruvic aldehyde 
probably takes place under certain conditions, but this involves 
reduction and so is not to be expected in the normal course of 
glucose oxidation. The fate of pyruvic acid under normal con- 
ditions is probably to undergo further oxidation through acetic 
acid to carbonic acid and water. It is possible that acetalde- 
hyde or alcohol or both may intervene between pyruvic acid 
and acetic acid, and that formic acid may be produced as an 
intermediate step between acetic and carbonic acids. 

To summarize what now appears to be the most promising 
theory of the intermediary metabolism of carbohydrate, we 
may say that the glucose is first transformed, either directly or 
through glyceric aldehyde, into pyruvic aldehyde (methyl 
glyoxal), which may either be changed to lactic acid or oxidized 
directly to pyruvic acid that readily undergoes oxidation to 
carbon dioxide and water through steps not yet fully worked 
out. Lactic acid may also be converted into pyruvic acid and 
thus ultimately be completely oxidized. In case of excessive 
formation or inadequate oxidation, as in extreme muscular 
fatigue or asphyxial conditions, lactic acid may accum.ulate 
in the body or may be excreted unchanged. 



THE FATE OF THE FOODSTUFFS IN METABOLISM 109 
Glucose 

Glyceric aldehyde % Methyl glyoxal ^ Lactic acid 

\ / 

Pyruvic acid 

\ 

(Acetic aldehyde) 

\ 

(Acetic acid) 

\ 

(Formic acid?) 

Carbonic acid 

Whatever the exact mechanism of the process, a large part 
of the glucose brought by the blood is oxidized in the muscles 
to furnish energy, which appears as external or internal work. 

In general, the rate at which combustion takes place in the 
tissues depends upon the activity of the tissue cells, rather than 
upon the supply either of combustible matter or of oxygen. 
When a sufficient supply of oxygen is provided, any further 
increase has httle effect upon the rate of combustion, and, as 
we have seen, any excess of carbohydrate instead of being burned 
is stored as glycogen. But while the absorption of an abun- 
dance of carbohydrate does not greatly change the amount of 
combustion taking place in the body, it may result in the use 
of carbohydrate as fuel almost to the exclusion of fat for the 
time being, as is shown by observations upon the respiratory 
quotient. 

The respiratory quotient is the quotient obtained by di- 
viding the volume of carbon dioxide given off in respiration by 
the volume of oxygen consumed. That is — 

Volume of CO. produced ^ . Respiratory quotient." 
Volume of O2 consumed 



no CHEMISTRY OF FOOD AND NUTRITION 

The numerical value of this quotient will evidently depend 
upon the elementary composition of the materials burned. Car- 
bohydrates will yield a quotient of i.o since they contain hy- 
drogen and oxygen in proportions to form water, so that all 
oxygen used to burn carbohydrate goes to the making of carbon 
dioxide, and each molecule of O2 so consumed will yield one 
molecule of CO2, occupying (under the same conditions of 
temperature and pressure) the same amount of space as the 
oxygen consumed to produce it. Thus in burning a molecule 
of glucose, six molecules of oxygen are consumed and six mole- 
cules of carbon dioxide produced : 

CcHioOe + 6 Oo ^ 6 CO2 + 6 H2O. 

Here the volumes of oxygen and of carbon dioxide are equal 
and the respiratory quotient is i.e. 

Fats contain much more hydrogen than can be oxidized by 
the oxygen present in the molecule, and therefore a part of the 
oxygen used to burn fat goes to form water, so that the volume 
of oxygen consumed is greater than the volume of carbon di- 
oxide produced, which gives a respiratory quotient lower than 
1.0. The common fats of the body and of the food give quo- 
tients approximating 0.7. Thus the oxidation of stearin is 
represented by the equation : 

2C57H110O6 + 16302^ 114CO2 + 110H2O. 

Since 163 volumes of oxygen are consumed and 114 volumes 
of carbon dioxide produced, the respiratory quotient is 

— ^ = 0.699. 
163 

Proteins give quotients intermediate between those of car- 
bohydrates and fats, but if the amount of protein used in the 
body be determined by other methods (see Chapter VIII) 
and allowed for, one may then deduce from the respiratory 
quotient the proportions of carbohydrates and fats which are 



THE FATE OF THE FOODSTUFFS IN METABOLISM III 

being burned in the body at any given time. The body will 
show a respiratory quotient of i.o when burning carbohydrate 
alone, of 0.7 when burning fat alone, and of an intermediate 
value when both fat and carbohydrate are being burned. If, 
now, the respiratory quotient rises soon after the eating of 
carbohydrate food, it is evident that the carbohydrate is being 
used more freely and fat less freely than before. 

In an experiment by Magnus-Levy the subject before taking 
food showed a quotient of 0.77. He then ate 155 grams of cane 
sugar, after which the quotient was determined at intervals of 
an hour for 7 hours with the following results: i.oi, 0.89, 
0.89, 0.92, 0.82, 0.82, 0.79. The quotient here shows that 
within an hour after the sugar was eaten the body was making 
use of the carbohydrate to such an extent that fat either was 
not being used at all or was being formed from carbohydrate 
as fast as it was burned; and that for seven hours after the 
meal the body continued to use carbohydrate to a greater, and 
fat to a less, extent than was the case at the beginning of the 
experiment. 

It has been pointed out that, when carbohydrate is absorbed 
in larger quantity than is required to meet the body's immediate 
needs for fuel, the surplus normally accumulates as glycogen, 
which is stored conspicuously in the Hver, but also to a con- 
siderable extent in the muscles and other organs. The amount 
of carbohydrate which will be stored in the entire body after 
rest and Uberal feeding is estimated at 300 to 400 grams. Thus 
the total amount of carbohydrate which can be stored as such 
in the body is no more than is frequently taken in one day's 
food. 

When the supply of carbohydrate is so abundant that it 
continues in excess of the needs of the body and accumulates 
until the liver and muscles have no tendency to increase their 
store of glycogen, the further surplus of carbohydrate tends 
to be converted into fat. 



112 CHEMISTRY OF FOOD AND NUTRITION 

Production of Fat from Carbohydrate 

Experimental evidence of the transformation of carbohydrate 
into fat has been cited in Chapter II where it was shown that 
animals which fatten readily on carbohydrate food may store 
more body fat than could possibly be derived from the fats 
and proteins eaten ; that milch cows have yielded more fat in 
the milk than could be accounted for on any other assumption 
than that fat was formed from carbohydrate; and that there 
may be more carbon stored in the body from the carbohydrate 
food eaten by a fattening animal than can be accounted for 
in any other way than that a part of the carbon taken into the 
body as carbohydrate was retained as body fat. 

Further proof of the ability of the animal body to change 
carbohydrate into fat is obtained from the respiratory quotient. 
As noted above, observations made after a fast tend to show 
quotients approaching that of fat, while after feeding carbohy- 
drates the quotient may rise rapidly. If the quotient reaches 
i.o, it shows that the body as a whole is using carbohydrate 
and not fat as fuel; and a quotient greater than i.o may be 
taken as evidence that the carbohydrate is itself supplying part 
of the oxygen which appears as carbon dioxide, or, in other 
words, that it is breaking down in such a way that a part is 
burned while another part goes to form in the body a substance 
more highly carbonaceous and having a lower respiratory 
quotient than the carbohydrate itself. In many cases it is 
certain that this substance can be nothing but fat. Respiratory 
quotients greater than i.o have been observed after Hberal 
carbohydrate feeding in several species, including man. Each 
such observation furnishes evidence of a conversion of car- 
bohydrate into fat. 

The formation of fat from carbohydrate in the animal body 
is therefore established by four distinct lines of experimental 
evidence: (i) by determination of the amounts of body fat 



THE FATE OF THE FOODSTUFFS IN METABOLISM II3 

formed, (2) by determination of the milk fat produced, (3) by 
observation of the amount of carbon stored, (4) by observations 
upon the respiratory quotient. 

Chemical Steps in the Formation of Fat from Carbohydrate 

While there is no doubt whatever of the ability of the animal 
to synthesize fat from carbohydrate, the mechanism of the pro- 
cess is far from clear. As expressed by Leathes, " the chemical 
changes involved are fascinating in their obscurity." What- 
ever the exact steps, the transformation of carbohydrate into 
fatty acid radicles must involve reduction of hydroxyl groups 
and condensations to form the long chains of the higher fatty 
acids. We have already seen that in what we believe to be the 
normal course of carbohydrate catabolism there occurs, either 
along with or quickly following the breaking of the glucose 
molecule into three-carbon compounds, a reduction of certain 
hydroxyl groups with transfer of the oxygen so that substances 
such as methyl glyoxal, pyruvic acid, and lactic acid are formed. 
From pyruvic acid or lactic acid acetaldehyde may be formed ; 
two molecules of acetaldehyde may then undergo aldol conden- 
sation and the aldol be transformed (by simultaneous reduction 
and oxidation, or transfer of oxygen from the ^ to the terminal 
carbon) into butyric acid. Such an hypothesis is consistent 
with reactions observed in vitro and with the well-known pro- 
duction of butyric acid in certain bacterial fermentations of 
sugar and of lactic acid. Leathes favors this hypothesis and 
comments upon it (in part) as follows : " The biochemical sig- 
nificance of the synthesis of butyric acid from lactic acid and 
from sugar by bacteria, becomes greater, however, when it is 
remembered that in this fermentation normal caproic acid is 
simultaneously formed, and as Raper showed also, though in 
still smaller amount, normal octoic or capryHc acid. ... In 
butyric fermentation it seems that the reactions that lead to 
the synthesis of butyric acid may lead to the synthesis of acids 



114 CHEMISTRY OF FOOD AND NUTRITION 

of longer chains but still unbranchcd and containing an even 
number of carbon atoms, in other words, that these acids may 
be produced by. condensation of two, three, or four acetic alde- 
hyde molecules. In higher organisms, plants or animals, this 
same condensation carried further would result as Nencki sug- 
gested in the formation of the series of acids with straight chains 
of even numbers of carbon atoms leading up to palmitic and 
stearic acid." Raper^ has shown experimentally that con- 
densation of two molecules of aldol in alkaline solution yields a 
straight chain product which on oxidation and reduction by 
laboratory methods yields normal octoic (caprylic) acid. 

Smedley has developed an alternative hypothesis regarding 
the mechanism of fatty acid synthesis from carbohydrate 
material. 

According to Smedley,^ the most probable starting point is 
pyruvic acid. 

As an intermediary step in the metabolism of carbohydrate, 
pyruvic acid is probably formed in large quantities in the 
body, though its reactivity may prevent it from accumulating 
in measurable amounts. 

Pyruvic acid readily breaks down to acetaldehyde and 
carbon dioxide. It also condenses with aldehydes to form prod- 
ucts which, under conditions similar to those existing in the 
body, undergo rearrangements (through simultaneous or suc- 
cessive oxidation and reduction) which result in the spHtting 
out of carbon dioxide leaving an acid of two more carbon atoms 
than were contained in the original aldehyde ; or an aldehyde 
of two more carbon atoms than the original aldehyde may be 
formed, and this in turn react with another molecule of pyruvic 
acid forming a fatty acid or aldehyde of two more carbon atoms. 

Each of these hypotheses assumes as a starting point only 

' /. Chem. Soc, Vol. 91, page 1831 (1907). See also Leathes, The Pats, pages 
106-109. 

"^Journal of Physiology, Vol. 45, Proc. page 26; Biochemical Journal, Vol. 7, 
pagj 364. 



THE FATE OF THE FOODSTUFFS IN METABOLISM 115 

substances which we have good reason to beheve are regularly 
formed in carbohydrate metabolism, and both are consistent 
with the well-known fact that natural fats contain fatty acid 
radicles having all multiples of two carbon atoms from four 
to eighteen, but none containing uneven numbers of carbon 
atoms in the molecule. 

FAT 

In digestion the fat is split into fatty acids and glycerol 
which, however, upon absorption are recombined into neutral 
fat. It is believed that this recombination occurs during the 
passage of these digestion products through the intestinal 
wall. The fat thus absorbed is taken up by the lymph vessels 
rather than the capillary blood vessels, and is poured with the 
lymph into the blood. The fat which renders the blood plasma 
turbid at the height of absorption will usually have passed from 
the blood into the tissues after a few hours. The fat thus 
leaving the blood may be burned as fuel, or stored for use as 
fuel in the future, and a part may be transformed into tissue 
lipoid or enter into combination with proteins to form some of the 
chemically more complex substances of cellular protoplasm, cell 
membrane, or of the central nervous system. The fat burned 
as fuel serves as a source of energy for muscular work and other 
activities essentially as does carbohydrate. The average re- 
sults of a very complete series of experiments by Atwater and 
his associates indicated that the potential energy of fat was 
95.5 per cent as efficient as that of carbohydrates for the pro- 
duction of muscular work. 

Oxidation of Fat 

The glycerol from fat is presumably oxidized to glyceric alde- 
hyde which passes to methyl glyoxal, whose fate is doubtless 
the same in this case as when the same substance is formed in 
carbohydrate metabolism. 



Il6 CHEMISTRY OF FOOD AND NUTRITION 

The fatty acid presents a separate problem. Through the 
work of Dakin, and of Knoop and Embden the " beta-oxidation 
theory " has been developed and is now generally accepted. Ac- 
cording to this theory the fatty acid is attacked by oxidation at the 
^-carbon atom with the probable formation first of /3-hydroxy, 
and then of )8-ke tonic acids. Further oxidation at this point must 
then cause a separation of the a- and y8-carbon atoms ; thus two 
carbons of the original fatty acid break away, presumably to un- 
dergo complete oxidation, and there remains a fatty acid with two 
less carbon atoms than the original. By such a process stearic 
acid would yield palmitic ; palmitic would yield myristic ; myris- 
tic, lauric ; and so on to butyric acid. Beta-oxidation of butyric 
acid would yield successively y8-oxybutyric, and acetoacetic acid. 
Normally the acetoacetic acid should yield two molecules of 
acetic, which in turn should burn to carbon dioxide and water. 

The sequence of changes from caproic acid to the final oxida- 
tion products would thus be as follows : 



Caproic 


; ^-oxY 


/3-KETO 


Butyric 


j3-0XY AcETO- Acetic Carboni 


ACID 


(hydroxy) 


CAPROIC 




butyric acetic 


CH3 


->CH3 ->CH3 

1 ' 


^CH3 


->CH3 ->CH3 ^2CH3 ->4C02 


CH2 


CH2 


CH2 


CH2 


CHOH CO2 COOH -I-4H2O 

1 1 


CH2 

1 


CH2 


CH2 


CH2 


CH2 CH2 

1 1 


1 
CH2 

1 


CHOH 


CO 


COOH 


COOH COOH 


1 
CH2 


CH2 


CH2 







COOH COOH COOH 

When the normal process is interfered with or overtaxed, an- 
other reaction may occur with the formation from acetoacetic 
acid of carbon dioxide and acetone, which latter like acetoacetic 
acid and j8-oxybutyric acid sometimes appears in the urine, 
especially in many cases of diabetes mellitus. The acidosis of 
diabetes is believed to be due to the )8-oxybutyric acid and 
acetoacetic acid thus formed. Acetone, acetoacetic acid, and 



THE FATE OF THE FOODSTUFFS IN METABOLISM 1 17 

/8-oxybutyric acid are sometimes spoken of collectively as " ace- 
tone bodies." For further discussion of the intermediary metab- 
olism of fat and of the evidence that the acidosis of diabetes 
is cliiefly due to acids arising from fat metabolism, the reader 
is referred to Dakin's Oxidations and Reductions in the Animal 
Body and the chapter on diabetes in Lusk's Science of Nutrition. 

Storage of Food Fat in the Body 

That fat derived from the food may be stored as body fat 
has already been shown (Chapter III) and need not be dis- 
cussed further here. Recently Mills ^ has found that fatty 
oils injected with antiseptic precautions into the subcutaneous 
tissue may under favorable conditions be absorbed therefrom 
and used in the body in the same way as if obtained by feeding. 
Whether fat once deposited in the tissues will remain and ac- 
cumulate, or be returned to the circulation and used as fuel, 
will depend upon the balance between the food consumption 
and the food requirements of the organism as a whole. In this 
respect, there is no difference between fat consumed and de- 
posited as such and fat formed in the body from other food 
materials. 

Can Carbohydrate be Formed from Fat? 

Glycerol is readily convertible into glucose in the body, 
probably passing through the form of glyceric aldehyde as an 
intermediate step; but the glycerol radicle represents only 
about one twentieth of the energy value of the fat molecule. 

Whether carbohydrate is ever formed from fatty acid in the 
animal body is an open question. 

As evidence of such formation of carbohydrate from fat, 
Hill cites observations upon hibernating animals showing in- 
crease of glycogen during sleep, accompanied by respiratory 
quotients lower than 0.7. 

^Archives of Internal Medicine, Vol. 7, page 6g4 (igii). 



Il8 CHEMISTRY OF FOOD AND NUTRITION 

On the other hand, in phlorizin poisoning * and severe diabetes 
when it would seem that all material in the body capable of 
transformation into glucose is being thus changed, there does 
not appear to be a production of glucose from fat (fatty acid). 
As this latter type of experimentation has been extensively em- 
ployed while relatively little evidence of the sort cited by Hill 
has been presented, the trend of opinion is rather away from the 
view that the animal body can form carbohydrate from fatty 
acid radicles, or transform fat into carbohydrate beyond the 
limited amount obtainable from the glyceryl radicles of the 
fat. It has been suggested that the low respiratory quotients 
above mentioned may be due to accidental fluctuations, since 
the blood does not always show the same carbon dioxide con- 
tent. The question of actual transformation of fat into car- 
bohydrate is not of great practical importance in normal nu- 
trition, because under normal conditions fats may be used 
interchangeably with carbohydrates as source of energy to a 
very large, though not unlimited, extent. 

PROTEINS 

It is now believed that the hydrolysis of proteins to amino 
acids in the digestive tract is practically complete. The sig- 
nificance of this digestive cleavage lies not simply in the for- 
mation of more soluble and more readily diffusible substances, 
but also in the resolution of the complex molecules of food 
protein into their simple amino acid " building stones " (" Bau- 
steine ") which may be rearranged by the body in the synthesis 
of its own tissue proteins. 

* Phlorizin causes very great glj-cosuria and, if the poisoning is continued, the 
usual symptoms of severe diabetes such as muscular weakness, acidosis, acetonuria, 
and death in coma. From moderate dosage, however, the animal recovers. The 
glucose content of the blood falls (instead of rising as in true diabetes). The action 
of the phlorizin appears to be primarily upon the kidneys, causing them to secrete 
glucose much more rapidly than usual, thus draining ofif the glucose from the blood 
and keeping it below the norma! level. 



THE FATE OF THE FOODSTUFFS IN METABOLISM 119 

Absorption and Distribution of Protein Digestion Products 

The work of the past few years, to be described in the para- 
graphs which follow, indicates that the amino acids, resulting 
from digestive hydrolysis of the food proteins, pass through the 
intestinal wall and into the blood of the portal vein unchanged, 
are carried through the liver into the blood of the general cir- 
culation and are thus distributed throughout the body, and are 
rapidly absorbed from the blood into the various tissues. Thus 
each tissue receives its protein material in the form of amino 
acids from which can be synthesized the particular kind of 
protein characteristic of the tissue in question. In other words, 
each tissue makes its own proteins from the amino acids brought 
by the blood. Amino acids not used in synthesizing protein 
(whether brought by the blood or formed by breakdown of 
tissue material) are broken down or deaminized in the tissues 
in the manner described beyond. 

A brief account of recent work on the distribution and im- 
mediate fate of the amino acids may serve to give a more ade- 
quate impression of the modern view. 

In 1906 Howell obtained a qualitative reaction for amino acids 
in the blood, but conclusive evidence of the relation of these 
amino acids to metabolism required the development of better 
methods than were then available for the estimation of amino acid 
nitrogen in the fluids and tissues of the body. Such methods were 
developed and appHed independently and almost simultaneously 
in 191 2 by FoUn and Denis and by Van Slyke and Meyer. 

Folin and Denis distinguished between the nitrogen of pro- 
teins, non-proteins, ammonia, and urea. The non-protein 
nitrogen includes that of amino acids and they were able to 
show that this form of nitrogen increased in the blood and 
tissues when glycine or a mixture of amino acids resulting 
from pancreatic digestion of protein was undergoing absorption 
from the small intestine. Moreover the increase in the non- 



120 CHEMISTRY OF FOOD AND NUTRITION 

protein nitrogen of the blood and muscles was nearly suflEicient 
to account for the nitrogenous material absorbed from the 
intestine, from which it appeared that they had traced the ab- 
sorbed amino acids and found them to be carried through the 
blood and to the muscles without being either built up into 
protein or broken down into ammonia or urea on the way. 
Urea formation was found to follow distinctly later than the 
absorption and distribution of the amino acids. 

Van Slyke and Meyer estimated amino acids by quantita- 
tive determination of the nitrogen present as amino groups in 
the non-protein fraction of the blood or tissue. They found 
that, during the digestion of protein, amino acids pass through 
the intestinal wall and appear not only in the portal blood but 
also in the blood of the general circulation, showing that the 
amino acids, for the most part at least, pass both the intestinal 
wall and the liver unchanged. 

Closely following the work of Folin and of Van Slyke, Rona 
(191 2) demonstrated by experiments upon isolated segments of 
intestine that the amino acids pass unchanged through the 
intestinal wall ; Abel (1913) dialyzed free amino acids from the 
circulating blood of living animals by means of his vivi-diffusion 
apparatus and actually separated alanine in crystaUine form; 
and Abderhalden (1914) separated glycine, alanine, valine, 
leucine, aspartic acid, glutamic acid, lysine, arginine, histidine, 
and tryptophane from large quantities of shed blood. Soon 
afterward (191 5) Henriques and Andersen showed that dogs 
and goats could be kept in a normal condition of nutrition and 
might even store nitrogen and gain weight when they were 
nourished exclusively by intravenous injection of a food solution 
containing nitrogen only in the form of completely digested 
protein — a strong confirmation both of the completeness of 
cleavage of protein in normal digestion and of the fact that the 
body is nourished by free amino acids carried by the blood with- 
out intervention of chemical changes in the intestinal wall. 



THE FATE OF THE FOODSTUFFS IN METABOLISM I2l 

Van Slyke (working upon dogs) continued his investigation 
of the fate of the amino acids and found that they are rapidly 
taken up from the blood by the tissues where they seem to be 
held by adsorption. Since the amino acids can be extracted 
by means of cold water or alcohol they do not seem to be held 
in chemical combination with the tissue proteins nor can simple 
diffusion account for the extent to which they enter the tissues, 
because they rapidly attain a higher concentration in the muscle 
and liver cells than in the blood with which these are in contact. 
The extent to which this concentration of amino acids in the 
muscles may go seems to have a fairly definite limit at about 
75 milligrams of amino acid nitrogen per loo grams of muscle. 
In the case of liver tissue this " saturation capacity " seems 
somewhat more elastic and the concentration may reach about 
twice the maximum observed in muscle, i.e. up to 150 miUi- 
grams of amino acid nitrogen per 100 grams of liver. In the 
muscles the amino acids taken up as just described disappear 
only very gradually and may not seem to be appreciably 
changed for several hours ; in the liver they disappear rapidly ; 
in the kidney, pancreas, and spleen they disappear less rapidly 
than in the liver. 

The disappearance of the amino acids from the tissues may 
be due either to a building up into protein or a breaking down 
with the formation of ammonia and urea or both. It seems 
probable that in general both processes go on in all tissues, 
each tissue building its own proteins and each also taking part 
in the deaminization of amino acids with formation of am- 
monia or urea. The more rapid disappearance of amino acids 
from the Hver tissue is probably due to the greater activity of 
the liver in deaminization and urea formation, especially since 
Van Slyke has recently measured the increase of urea in the 
blood on its passage through the Hver and shown that the 
passage of the blood through the muscle under parallel con- 
ditions does not increase its urea content to a measurable extent. 



122 CHEMISTRY OF FOOD AND NUTRITION 

Van Slyke's experiments also show that the blood contains 
amino acids at all times and that the tissues are not freed from 
amino acids by fasting, while on the other hand high protein 
feeding does not result in any great accumulation of amino 
acids as such either in the blood or tissues. All these observa- 
tions confirm the view that amino acids are the normal inter- 
mediary products in both the building up and breaking down of 
body protein and that any large storage of nitrogen in the body 
must be due to formation of body protein and not to mere ac- 
cumulation of free amino acids. 

Utilization of Protein in the Tissues 

The proteins of the digested food, absorbed and distributed 
in the form of amino acids as described above, soon become 
available for nutrition ; and among other functions they, like 
the carbohydrates and fats, may be burned * as fuel for muscular 
work. Pfiuger proved that protein may serve as a source of 
muscular energy by feeding a dog for 7 months exclusively upon 
meat practically free from fat and carbohydrate, and requiring 
it throughout the experiment to do considerable amounts of 
work, the energy for which must in this particular case have 
been derived largely from the protein consumed. 

The experimental facts and theoretical explanations regard- 
ing the breaking down of proteins (or of the amino acids arising 
from them) in the body tissues must now be considered. By 
experiment it has been found that if a meal extra rich in pro- 
tein be eaten, an increased elimination of nitrogenous end pro- 
ducts can be observed within 2 or 3 hours, and probably much 
the greater part of the surplus nitrogen will have been excreted 
within 24 hours of the time it was taken into the stomach. It 
does not follow, however, that the whole of the protein mole- 

* It will of course be understood that the protein is not supposed to be burned 
directly. Protein is split to amino acids, the amino acids deaminized, and the non- 
nitrogenous residues of the amino acids are burned. 



THE FATE OE THE FOODSTUFFS IN METABOLISM 1 23 

cule is broken down and eliminated so quickly, and many ex- 
periments have shown that the carbon often does not leave the 
body so rapidly as does the nitrogen. Evidently, the nitrog- 
enous radicles of the protein may be split off in such a way as 
to leave a non-nitrogenous residue in the body, and the study of 
protein metabolism involves a consideration of the fate of 
both the nitrogenous and the non-nitrogenous derivatives. 
The fate of the latter may conveniently be considered first 
on account of its relation to the metabolism of carbohydrates 
and fats. Of special interest is the problem to what extent the 
deaminized cleavage products of protein may be actually trans- 
formed into carbohydrate or fat in the body. 

Formation of Carbohydrate from Protein 

As early as 1876 Wolff berg tested the formation of carbohy- 
drate from protein by fasting fowls for two days in order to 
free them from glycogen and then feeding for two days with 
meat powder which had been washed free from carbohydrate. 
Two of the fowls were killed soon after this protein feeding 
and showed more glycogen in their livers and muscles than could 
be accounted for except as derived from the protein fed. Two 
similar fowls killed 17 and 24 hours after feeding showed much 
less glycogen. This formation of glycogen from protein was 
fully confirmed by Kulz in a long series of experiments in which 
the food consisted of chopped meat thoroughly extracted with 
warm water (Lusk). 

Independent evidence of the production of carbohydrates 
from protein is found in the work of Seegen, who chopped and 
mixed the liver of a freshly killed animal and determined the 
amount of carbohydrate in it by analysis of a portion, while 
the remainder was kept at body temperature and sampled for 
analysis from time to time. The percentage of carbohydrate 
was found to increase, showing that the Hver cells can form car- 
bohydrate from their own protein substance. 



124 CHEMISTRY OF FOOD AND NUTRITION 

The most striking evidence of the origin of carbohydrate from 
protein in the animal body is found in the many observations 
and experiments which have been made in cases of diabetes, 
and in experimental glycosuria produced either by administra- 
tion of phlorizin or by removal of the pancreas. In such cases 
large amounts of carbohydrate may be given off in the form of 
glucose even when there is Httle body fat and no carbohydrate 
or fat is fed. The glucose must therefore result from the me- 
tabolism of protein. In Lusk's exhaustive experiments upon 
dogs rendered diabetic by phlorizin, 58 per cent of the total 
weight of protein broken down in the body (whether in 
fasting or on a meat diet) Was eliminated in the form of 
glucose. According to Lusk : " After ingestion of protein in 
the normal organism this sugar becomes early available and 
may be burned before the nitrogen belonging to it is ehmi- 
nated, or, if the sugar be formed in excess, it may be stored 
as glycogen in the liver and muscles for subsequent use. In 
this way it is obvious that at least half the energy in protein 
may be independent of the curve of nitrogen elimination, but 
may rather act as though it had been ingested in the form of 
carbohydrates." 

The way in which the production of carbohydrate from pro- 
tein may take place has received much attention. Lusk dem- 
onstrated experimentally that alanine, one of the cleavage prod- 
ucts of all known proteins, may yield glucose abundantly in 
the body ; and he suggested that the change might occur through 
the formation of lactic acid as an intermediary product, since 
he had already shown that lactic acid is convertible into glu- 
cose. The work of Dakin has thrown further light on the 
intermediate steps of this transformation. He has shown that 
glyoxals have been formed from a-amino and a-hydroxy acids, 
in vitro — e.g. pyruvic aldehyde (methyl glyoxal) from alanine 
and lactic acid ; and on the other hand a-hydroxy acids have 
been formed from glyoxals, both in vivo and in vitro. 



THE FATE OF THE FOODSTUFFS IN METABOLISM 125 
CH3— CHNH2— COOH^ CH3— CO— CHO + NH3 

Alanine Methyl glyoxal 

CH3— CHOH— COOH t CH3— CO— CHO + H2O 

Lactic acid Methyl glyoxal 

Attempts, however, to synthesize amino acids directly from 
glyoxals in vitro were not successful. There is some evidence 
of that synthesis in vivo, but it cannot be considered as fully 
established whether it takes place directly by the addition of 
ammonia to free glyoxals, or whether the a-amino acid is formed 
secondarily from the a-ketonic acid, resulting from the oxidation 
of glyoxals. The work of Knoop and of Embden and Schmitz 
leaves no doubt of the ability of the liver cells to form amino 
acids from the ammonium salts of the corresponding a-ketonic 
acids. Alanine, phenylalanine, and tyrosine were produced in 
this way.* It is of course possible that there may have occurred, 
in these liver perfusion experiments, intermediate steps not 
recognized by the investigators, but this does not detract from 
the significance of the fact that the synthesis of amino acids 
from ammonium salts has now been repeatedly demonstrated 
by experiment. 

The relations emphasized by Dakin may be represented as 
follows : 

Glucose Protein 

I i II 

(Glyceric aldehyde ?) (Amino acids including) 

II II 
Lactic acid ^ Methyl glyoxal J5?^ Alanine 

^\ I ^^^ 

^^ Pyruvic acid^-""'^ 

I 
to further oxidation 

* Embden also obtained alanine after perfusion of ammonium lactate, but the 
lactate may have been first changed to pyruvate and the alanine formed from the 
latter. 



126 CHEMISTRY OF FOOD AND NUTRITION 

Attention may be called in passing to the possible importance 
of the interrelations of alanine, methyl glyoxal, and lactic 
acid to the regulation of neutrality, not only in the body as a 
whole (Chapter IX) but also in the particular cells in which 
deamination may be more active than oxidation. It will be 
noted that alanine (a nearly neutral substance) yields on de- 
amination another neutral suljstance (methyl glyoxal) and a 
base (ammonia) 

CH3— CHNHo— COOH -^ CH3— CO— CHO + NH3 

And furthermore that the neutral substance methyl glyoxal 
may react with water to form lactic acid 

CH3— CO— CHO + H-.O ->- CHa- CHOH— COOH 

Experiments in vitro have shown that the production of 
lactic acid from methyl glyoxal is promptly checked unless the 
free acid is quickly neutraHzed ; also that the conversion of 
alanine into methyl glyoxal and ammonia is accelerated by acids 
(Dakin). 

Thus far the possible mechanism of formation of carbohydrate 
from protein cleavage products has been considered here chiefly 
in terms of alanine. To what extent is its behavior representa- 
tive of that of the other amino acids? Experiments in vitro 
show that the transformation of an a-amino acid into the cor- 
responding a-ketonic aldehyde is a very general reaction. Dakin 
and Dudley demonstrated it for all the amino acids with which 
they worked — glycine, alanine, phenylalanine, vaUne, leucine, 
and aspartic acid. Experiments in vivo (chiefly on dogs ren- 
dered diabetic by phlorizin poisoning) have shown that glycine, 
alanine, serine, cystine, aspartic acid, glutamic acid, arginine, 
and proline are all capable of yielding large amounts of glu- 
cose. Leucine, tyrosine, and phenylalanine when similarly 
administered to phlorizinized dogs increase the elimination of 
acetoacetic acid rather than glucose. Valine, lysine, and 



THE FATE OF THE FOODSTUFFS IN METABOLISM 1 27 

tryptophane yield neither glucose nor acetoacetic acid to any 
important extent (Dakin). 

The amino acids which yield glucose are called glucogenetic, 
and the amount of glucose which a given protein can yield in 
the body will naturally depend upon the glucogenetic amino 
acid radicles which it contains. Since the amino acids result- 
ing from protein hydrolysis cannot be quantitatively recovered 
by any laboratory method thus far developed, it is not yet 
possible to calculate just how much carbohydrate a given protein 
should theoretically yield. For meat protein and some others 
the yield has been determined experimentally as in Lusk's in- 
vestigations cited above. For further discussion of this point 
see Lusk's Science of Nutrition. 

We have therefore abundant evidence from the work of in- 
dependent investigators, using different methods, that the 
animal body may form carbohydrates readily and in large pro- 
portion from the protein of the food; and the mechanism of 
the process is beginning to be fairly well understood. 

Production of Fat from Protein 

There has been much controversy regarding the formation 
of fat from protein in the animal body. A number of observa- 
tions by Voit which were believed to demonstrate such a pro- 
duction of fat were subjected to vigorous criticism by Pfliiger 
and apparently shown to be capable of other interpretations. 
Later experiments by Cremer in Voit's laboratory appear, 
however, to estabHsh the 'formation of body fat from protein 
food beyond reasonable doubt. 

Thus in one of these experiments a cat after a preliminary 
period of fasting was placed in a respiration apparatus and 
fed hberally with lean meat for eight days. The amount of 
protein broken down in the body was estimated from the nitro- 
gen eliminated. The carbon eliminated was also measured, 



128 CHEMISTRY OF FOOD AND NUTRITION 

and it was found that 58.4 grams of carbon had been retained 
in the body. This would correspond to 130 grams of glycogen, 
but the total amount of glycogen in the body at the end of the 
experiment was only 35 grams, hence about three fourths of 
the carbon retained by the cat from the protein food must 
have been stored as body fat. 

The evidence of formation of milk fat in part from protein, 
while perhaps not amounting to a mathematical demonstration, 
is still very strong. 

Since there is already abundant experimental evidence of the 
production of carbohydrate from protein and of the transfor- 
mation of carbohydrate into fat, it is evident that protein food 
can indirectly, if not directly, contribute to the formation of 
fat in the body. 

The Fate of the Nitrogen in Protein Metabolism 

It has already been shown that the nitrogen of the protein 
of food enters the circulation chiefly, if not wholly, as amino acids 
and is taken up as amino acids by the various body tissues. 
The amino acids thus obtained by the tissues from the food 
serve as material for the building up of body proteins; but in 
the breaking down of body proteins there is doubtless a liber- 
ation of amino acids of the same kinds. Amino acids from 
either source are subject to deaminization in the tissues, and in 
so far as a-amino groups are concerned the process doubtless 
consists chiefly in the splitting out of the nitrogen as ammonia, 
most of which is later changed to urea. Nitrogen in other 
forms than a-amino acids may be expected to undergo a some- 
what different metabolism, and it is well known that the urine 
always contains other nitrogen compounds in addition to 
ammonium salts and urea. 

Much light has been thrown upon the chemistry of protein 
metabolism by the study of the quantitative relations existing 



THE FATE OF THE FOODSTUFFS IN METABOLISM 1 29 

among the different forms of nitrogen in the urine under dif- 
ferent conditions. For our present purpose it will be sufficient 
to consider only the more important of the nitrogen compounds 
of the urine and the relations which they are beUeved to bear 
to the processes of normal metabolism. 

Urea. — The proteins, on being metaboUzed in the body, 
yield varying amounts of arginine, which may undergo hydroly- 
sis into ornithine and urea. In this way a small part of the 
nitrogen of protein may reach the urea stage through a series 
of direct cleavages. It is altogether probable, however, that 
much the greater part of the urea ehminated arises as follows : 
The protein in cataboHsm is split to amino acids, which are 
deaminized (as in the conversion of alanine to methyl glyoxal 
above mentioned), the nitrogen of the amino group being spHt 
out as ammonia, which with the carbonic acid constantly being 
produced in metabolism forms ammonium carbonate.* Loss 
of one molecule of water yields ammonium carbamate, which 
in turn on loss of one molecule of water yields urea. 

(NH4)2C03 ^ NH4CO2NH2 + H2O 

NH4C02NH2^CO(NH2)2 + H2O 

Ammonium chloride or sulphate evidently cannot be changed 
to urea in this way ; and experiments show that if hydrochloric 
or sulphuric acid is introduced into the blood, it is eliminated 
by the kidneys largely as ammonium salt, and the quantity of 
urea is correspondingly decreased. In diseased conditions of 
the liver the organic salts of ammonia (which normally should 
be burned to carbonate and then converted as above) may also 
pass through and be eliminated without being changed to urea. 
In health and on a full protein diet (say about 100 grams protein 
per day) from 82 to 88 per cent of the total nitrogen excreted 
by the kidneys is usually in the form of urea. On a low protein 
diet this percentage is lower. 

* If ammonium salts of organic acids are first formed, the complete oxidation 
of the organic acid radicle will bring this ammonia also into the form of carbonate. 
K 



I30 CHEMISTRY OF FOOD AND NUTRITION 

Ammonia. — As already noted, ammonia is evidently a 
normal precursor of urea, being changed to the latter in part 
in the muscles and other tissues generally and in part during 
its passage through the liver. In accordance with this view 
we find that the eUmination of nitrogen as ammonia may be 
notably increased at the expense of urea : (i) in structural dis- 
eases of the liver; (2) after injecting mineral acids which 
combine with ammonia in the body, forming stable ammonium 
salts ; (3) in cases of a pathological excess of acids in metabolism, 
such as often occurs in diabetes and in fevers. All of these are, 
of course, abnormal conditions. Normally, about 2 to 6 per cent 
of the total nitrogen eliminated is in the form of ammonium 
salts, the amount depending largely upon the relation between 
the amounts of acid-forming and of base-forming elements in 
the food, which will be discussed in connection with the study 
of the ash constituents of food and of mineral metabolism 
(Chapter X). 

Uric acid and the purine bases (nucleic acid metabolism). — 
A part of the nitrogen of human urine is always in the form of 
uric acid and purine bases. These owe their origin either to 
the free purine substances of the food, such as the guanine and 
hypoxanthine of meat extract, or to the metabohsm of nucleic 
acid derived from the nucleoproteins of the food or of the body 
tissues. The constituent groups of the nucleic acids and the 
order of their liberation on hydrolytic cleavage such as occurs 
in metabolism may be represented by the following diagram 
adapted from the works of Wells and of Jones : 



THE FATE OF THE FOODSTUFFS IN METABOLISM 131 
Nucleoprotein 

Protein Nuclein 

Protein Nucleic acid {Nucleotide) 

Phosphoric acid Nucleoside 

Carbohydrate 

Purine bases 

Adenine 

Guanine 

Base<| Pyrimidine bases 

Cytosine 

Thymine 

Uracil 

Explanation of diagram. — The distinction between nucleo- 
proteins and nucleins is somewhat arbitrary and perhaps of 
doubtful value. Wells regards nucleoproteins simply as com- 
plexes containing a larger proportion of protein than is con- 
tained in nucleins or vice versa. Jones prefers to discuss nuclein 
metabolism entirely in terms of nucleic acid in order to avoid 
the danger of unnecessary confusion with protein metabolism. 
The nucleic acids do not contain any radicles found in simple 
proteins ; they are compounds of phosphoric acid and carbohy- 
drate with purine and pyrimidine bases in which the acid and 
base radicles are not linked to each other but both to the car- 
bohydrate radicle. Phosphoric acid-carbohydrate-base chains 
of this sort are called nucleotides, and the nucleic acids contain- 
ing four such chains in the molecule are, in this terminology, 
tetranucleotides. Nucleotidases are enzymes which split nucleic 
acids liberating the phosphoric acid and leaving compounds of 
carbohydrate with base which are collectively known as nucleo- 



132 CHEMISTRY OF FOOD AND NUTRITION 

sides. Nucleosidases are enzymes splitting nucleosides into 
their constituent carbohydrates and bases. In the case of plant 
nucleic acid the carbohydrate is a pentose ((/.ribose) and the 
bases are adenine, guanine, cytosine, and uracil. In animal 
nucleic acid the carbohydrate is that of a hexose and the bases 
are adenine, guanine, cytosine, and thymine. 

Lusk summarizes the hydrolysis of yeast nucleotides as 
follows : 

Nucleotide — H3PO4 ->- Nucleoside — c?.ribose ->■ Base 
Adenylic acid ->- Adenosine ->■ Adenine 

Guanylic acid ->■ Guanosine ->■ Guanine 

Cytodin-nucleotide ->- Cytodine ->- Cytosine 

Uridin-nucleotide ->- Uridine ->- Uracil 

And to show at a glance the characteristic cleavage products 
of the two types of nucleic acid : 

Animal nucleic acid Plant nucleic acid 

(Thymus) (Yeast) 

Phosphoric acid Phosphoric acid 

Guanine Guanine 

Adenine Adenine 

Cytosine Cytosine 

Thymine Uracil 

Hexose Pentose 

Formulce and relationships. — The chemical relationships 
of the purine bases and uric acid so far as these are shown by 
empirical formulae are as follows : 

Purine, C5H4N4 

Adenine, C5H3N4NH2, amino-purine 
Guanine, C5H3N4ONH2, amino-oxy-purine 
Hypoxanthine, C5H4N4O, oxy-purine 
Xanthine, C5H4N4O2, dioxy-purine 
Uric acid, C6H4N4O3, trioxy-purine 



THE FATE OF THE FOODSTUFFS IN METABOLISM 1 33 

Uric acid, the most highly oxidized of these purines, is the 
one chiefly found in the urine. 

The chemical relations of these substances to each other are 
more fully shown by the structural formulae given on this page. 

The chemical structure of the pyrimidine bases is indicated 
by the following formulae : 

Cytosine Thymine Uracil 

N= C— NH2 NH— CO NH— CO 

II II II 

CO CH CO C— CH3 CO CH 

I II ' I II I II 

NH— CH NH— CH NH— CH 

6-amino, 2-oxy-pyrimidine 5-methyl, 2, 6-dioxy-pyrimidine 2, 6-dioxy-pyrimidine 

Since these substances do not yield uric acid or purine bases 
their fate will not be discussed here. 

The mode of origin of uric acid from nucleic acid through the 
purine bases is as follows : 

Nucleic acid 



N = C— NHo 



HN— CO 



HC C— NH 



>CH 



N— C— N 

Adenine 
(6-amino purine) 



H2NC C— NH 

II II >CH 

N— C— N"^ 

Guanine 
(2-amino, 6-oxy purine) 



HN— CO 



NH— CO 



HN— CO 



HC C— NH— > 

II II >CH 
N— C— N^ 

Hypoxanthine 
(6-oxy purine) 



OC C— NH— > 

I II >CH 
HN— C— N^ 

Xanthine 
(2, 6-dioxy purine) 



OC C— NH 

I II >co 

HN— C— NH 

Uric acid 
(2, 6, 8-trioxy purine) 



134 CHEMISTRY OF TOOD AXl) XUTRITION 

Not only is uric acid the most highly oxidized of the purines, 
but it represents the highest degree to which oxidation can be 
carried without breaking the purine ring. The extent to which 
the purine ring is broken and uric acid destroyed in the body 
varies with the species. In most mammals such " uricolysis " 
is an important feature of the purine metabolism. In man the 
power to destroy uric acid seems to have been almost or en- 
tirely lost, many recent investigations tending to show that the 
human body does not contain uricolytic enzymes and that 
all of the uric acid formed in the body must be transported and 
excreted either through the kidneys (chiefly in the form of acid 
urates) or through the intestinal wall. 

Purines undergoing metabolism in the body may be derived 
either (i) from the catabolism of nucleoprotein of body tissue 
or (2) from the food which may contain both nucleoproteins 
and free purines. Sometimes the term " endogenous uric acid " 
is applied to that fraction having the former origin, while " ex- 
ogenous uric acid " indicates that fraction which is directly due 
to the food. The endogenous uric acid in the urine of man of 
average size amounts usually to about 0.3 to 0.4 gram per day ; 
the exogenous varies from mere traces to 2 grams or more accord- 
ing to the kind and amount of food consumed. On ordinary 
mixed diet the total urinary output of uric acid averages about 
0.6 to 0.7 gram per man per day. The usual range is about 
0.5 to i.o gram of uric acid per man per day, in which case the 
uric acid nitrogen constitutes about i to 3 per cent of the total 
nitrogen of the urine. 

Recent investigations of Jones, Levene, and others have 
greatly elaborated the theory of nucleic acid structure and 
purine metaboHsm outHned above. For full discussion the 
reader is referred to the works of Jones (1914) and Jones and 
Read (1917). 

Creatine and creatinine. — Chemically creatinine is the 
anhydride of creatine : 



THE FATE OF THE FOODSTUFFS IN METABOLISM 135 

N (CH3)— CH2— C =0 N (CH3)— CH2— CO 

I I I 

HN = C OH HN = C 

I I 

NH2 NH' 

Creatine Creatinine 

The biochemical relationships and physiological significance 
of these substances have been much studied in recent years, 
and the literature of the subject is far too extensive to be 
summarized satisfactorily here. The main facts with regard to 
their ehmination as end products of metaboHsm are : that crea- 
tine appears in the urine of children normally and in that of 
adults during starvation, fevers, and other wasting diseases 
and when there is impaired functioning of the liver ; that 
normal adults ordinarily excrete little or no creatine but a 
considerable amount of creatinine. The quantity of creatinine 
excreted is fairly constant for the individual, averaging about 
0.02 gram per kilogram of body weight per day. On ordinary 
mixed diet the creatinine nitrogen usually constitutes 3 to 7 
per cent of the total nitrogen of the urine. 

Distribution of excreted nitrogen as influenced by level of pro- 
tein metabolism. — The above statements regarding the dis- 
tribution of the eliminated nitrogen among the different end 
products refer to results obtained upon an ordinary mixed 
diet containing the usual amount of protein. FoUn has shown 
by a careful and extended study of the urines of healthy men 
living first upon high and then upon low protein diets, that the 
distribution of the nitrogen between urea and the other nitrog- 
enous end products depends very largely upon the absolute 
amount of nitrogen metaboUzed. In the case of a man who on 
one day consumed high protein diet free from meat, and a week 
later was living on a diet of starch and cream, which furnished 
in all about 6 grams of protein per day, the distribution of end 
products was changed as shown in the following table : 



136 



CHEMISTRY OF FOOD AND NUTRITION 



Total nitrogen . . 
Urea nitrogen . . 
Ammonia nitrogen 
Uric acid nitrogen 
Creatinine nitrogen 
Undetermined nitrogen 



On High Protein Diet 
(Free from Meat) 



Grams 



16.8 

14.7 
0.49 
0.18 
0.58 
0.85 



Per cent 



87.5 
2.9 
i.i 
3.6 
4-9 



On Low Protein Diet 
(Starch and Cream) 



Grams 



3.6 

2.2 

0.42 

0.09 

0.60 

0.27 



Per cent 



61.7 
"•3 

2-5 

17.2 
7-3 



Thus, on passing from the high protein to the low protein diet 
(both being free from meat products) there was a marked de- 
crease in both the absolute and the relative amounts of urea, 
and a decrease in the absolute, but increase in the relative, 
amount of uric acid, while the absolute amount of creatinine 
remained unchanged, so that its relative amount was greatly 
increased. 

REFERENCES 

Abderhalden. Lehrbuch der Physiologische Chemie, Dritte Aufl. 

Abel, Rowntree and Turner. The Removal of Diffusible Substances 

from the Circulating Blood of Living Animals by Dialysis. Journal 

of Pharmacology, Vol. 5, page 275 (1913). 
Ackroyd ANT) Hopkins. Feeding Experiments with Deficiencies in the 

Amino Acid Supply : Arginine and Histidine as Possible Precursors 

of Purines. Biochemical Journal, Vol. 10, pages 551-576 (December, 

1916). 
Allen. Glycosuria and Diabetes. 
Benedict. Uric Acid in Its Relations to Metabolism. The Harvey 

Lectures, 1915-1916. 
Dakin. Oxidations and Reductions in the Animal Body. 
Dakin and Dudley. (A series of papers on intermediary metabolism.) 

Journal of Biological Chemistry, Vol. 14, pages 321, 423, 555; Vol. 15, 

pages 127, 463; Vol. 16, page 505; Vol. 17, page 451; Vol. 18, page 

29 (1912-1913). 
Embden and Schmitz. Synthesis of Amino Acids in the Liver. Bio- 

ckemische Zeitschrifl, Vol. 29, page 423; Vol. 38, page 393 (1910-1912). 



THE FATE OF THE FOODSTUFFS IN METABOLISM 137 

FoLiN. A Theory of Protein Metabolism. American Journal of Physi- 
ology, Vol. 13, page 117 (1905). 

FoLiN AND Denis. Protein Metabolism from the Standpoint of Blood and 
Tissue Analysis. Journal of Biological Chemistry, Vol. 11, pages 87, 
161; Vol. 12, pages 141, 253, 259; Vol. 14, page 29 (1912-1913). 

Henriques and Andersen. Nutrition through Intravenous Injection. 
Zeilschrifl fur physiologische Chemic, Vol. 88, page 357 (1913). 

Janney. The Metabolic Relationship of the Proteins to Glucose. Journal 
of Biological Chemistry, Vol. 20, page 321 ; Vol. 22, page 203; Vol. 23, 
page 77 (iQiS)- 

Jones. Nucleic Acids ; their Chemical Properties and [Physiological 
Conduct (19 14). 

Jones and Read. (On the structure of yeast nucleic acid.) Journal of 
Biological Chemistry, Vol. 29, pages 111-122, 123-126; Vol. 31, page 
337 (1917)- 

Knoop ANT) Kertes. Behavior of a-Amino Acids and a-Ketonic Acids 
in the Liver. Zeitschrifl fiir physiologische Chemie, Vol. 71, page 252 
(1911). 

Levene and Meyer. (Intermediary metabolism of carbohydrate.) Jour- 
nal of Biological Chemistry, Vol. 1 1 , page 361; Vol. 1 2, page 265 ; Vol. 1 4, 
pages 149, 551; Vol. IS, page 65; Vol. 17, page 442; Vol. 18, page 
469 (1912-1914). 

LuSK. Science of Nutrition. 

Lyman. Metabolism of Fats. Journal of Biological Chemistry, Vol. 32, 
pages 7, 13 (1917)- 

Mathews. Physiological Chemistry, Chapter 18. 

Ffluger. Glycogen. Archiv fiir die gesammte Physiologic, Vol. 96, pages 
1-398 (1903). 

Rose. Creatinuria in Women. Journal of Biological Chemistry, Vol. 31, 
page I (1917)- 

Underbill. Studies on the Metabolism of Ammonium Salts. Journal 
of Biological Chemistry, Vol. 15, pages 327, 337, 341 (1913). 

Van Slyke. The Significance of Amino Acids in Physiology and Pa- 
thology. Harvey Lectures, 1915-1916. 

Van Slyke et al. The Fate of Protein Digestion Products in the Body. 
Journal of Biological Chemistry, Vol. 12, page 399; Vol. 16, pages 187, 
197, 213, 231 (1912-1913). Proceedings of the Society for Experimental 
Biology and Medicine, Vol. 12, page 93 (1915). 

Wells. Chemical Pathology. 

WooDYATT. Studies on Intermediary Carbohydrate Metabolism. Harvey 
Lectures, 1915-1916. 



CHAPTER VI 

THE FUEL VALUE OF FOOD AND THE ENERGY 
REQUIREMENT OF THE BODY 

We have seen that carbohydrate after its absorption into 
the body may either be oxidized, or stored as glycogen, or trans- 
formed into fat ; that fat may be oxidized or stored and that at 
least its glyceryl radicle may be converted into carbohydrate ; 
and that protein absorbed as amino acids may either be built 
up into body protein, or deaminized and oxidized, or may yield 
carbohydrate, or may (either directly or indirectly) contribute 
to the production of fat. It has also been shown that any or 
all of these foodstuffs may be utiUzed as fuel for muscular 
work. 

Thus the body is not restricted to the use of any one food- 
stuff for the support of any one kind of work, but on the contrary 
has very great power to convert one nutrient into, or use it in 
place of, another, and so to utilize its resources that the total 
potential energy of all of these nutrients is economically em- 
ployed to support the work of all parts of the organism. The 
carbohydrates, fats, and proteins stand in such close mutual 
relations in their service to the body that for many purposes 
we may properly consider the food as a whole with reference 
to the total nutritive requirements, provided a common meas- 
ure of values and requirements can be found. Since the 
most conspicuous nutritive requirement is that of energy for 
the work of the body, and since these organic nutrients all 

138 



THE FUEL VALUE OF FOOD 1 39 

serve as fuel to yield this energy, the best basis of comparison 
is that of fuel value, expressed most conveniently in terms of 
Calories. 

Heats of Combustion of the Foodstuffs 

The calorific value or heat of combustion of any substance, 
i.e. the amount of energy liberated by the burning of a given 
quantity of the combustible material, is best determined by 
means of the bomb calorimeter devised by Berthelot. The 
particular form of Berthelot bomb which has been most used 
in the examination of food materials and physiological products 
is that of Atwater and Blakeslee, fully described by Atwater 
and Snell in the Journal of the American Chemical Society for 
July, 1903. In outHne it consists of a heavy steel bomb with 
a platinum or gold-plated copper lining and a cover held tightly 
in place by means of a strong screw collar. A weighed amount 
of sample is placed in a capsule within the bomb, which is then 
charged with oxygen to a pressure of at least 20 atmospheres 
(300 pounds or more to the square inch), closed, and immersed 
in a weighed amount of water. The water is constantly stirred 
and its temperature taken at intervals of one minute by means 
of a differential thermometer capable of being read to one 
thousandth of a degree. After the rate at which the temperature 
of the water rises or falls has been determined, the sample 
is ignited by means of an electric fuse, and, on account of the 
large amount of oxygen present, undergoes rapid and complete 
combustion. The heat liberated is communicated to the water 
in which the bomb is immersed, and the resulting rise in tem- 
perature is accurately determined. The thermometer read- 
ings are also continued through an " after period," in order 
that the " radiation correction " may be calculated and the 
observed rise of temperature corrected accordingly. This 
corrected rise, multiplied by the total heat capacity of the ap- 
paratus and the water in which it is immersed, shows the total 



I40 



CHEMISTRY OF FOOD AND NUTRITION 



heat liberated in the bomb. From this must be deducted the 
heat arising from accessory combustions (the oxidation of the 

iron wire used as a 
fuse, etc.) to ob- 
tain the number of 
Calories * arising 
from the combus- 
tion of the sample. 
More recently 
the adiabatic form 
of the bomb cal- 
orimeter (a modifi- 
cation which avoids 
the necessity of cor- 
rections for heat 
loss) is coming into 
more general use. 
See, for example, 
the paper by Riche, 
in the Journal of the 
A merican Chemical 
Society for Novem- 
ber, 1913. 

* When the term " Cal- 
orie" is used in this work 
it will be understood to 
mean the "greater cal- 
orie," or "kilogram cal- 
orie," i.e. the amount of 
heat required l,to raise 
the temperature of one 
kilogram of water one 
degree centigrade. This 
is very nearly the same 
as the heat required to 
raise four pounds of water 
The Atwater bomb calorimeter. one degree Fahrenheit. 




THE FUEL VALUE OF FOOD 1 41 

The heat of combustion of organic substances is closely 
connected with their elementary composition. One gram 
of carbon burned to carbon dioxide ^-ields 8.08 Calories and 
I gram of hydrogen burned to water yields 34.5 Calories. If 
a compound consisting of carbon and hydrogen only be burned, 
it gives nearly the amount of heat which these would give if 
burned separately. 

On the other hand, carbohydrates and fats, being com- 
posed of carbon, hydrogen, and oxygen, the carbon and 
hydrogen are already partly oxidized by the oxygen present 
in the molecule ; so that 100 grams of glucose, for example, 
containing 40 grams carbon, 6.7 grams hydrogen, and 53.3 
grams oxygen, would yield considerably less heat than would 
be obtained by burning 40 grams of pure carbon and 6.7 
grams of pure hydrogen to carbon dioxide and water respec- 
tively. 

Proteins when burned in the calorimeter give ofiE their 
carbon as carbon dioxide, their hydrogen as water, and 
their nitrogen as nitrogen gas.* Thus the nitrogen con- 
tributes nothing to and takes nothing from the heat of com- 
bustion; and the latter is dependent here, as in the case of 
carbohydrates and fats, upon the amount of carbon and 
hydrogen present and the extent to which they are already 
combined with oxygen. A Httle additional heat is obtained 
by the burning of the small amount of sulphur present in the 
protein. 

The relation between the elementary composition and heat 
of combustion will be made clearer by the following table, 
which includes a number of typical compounds found in the 
food or formed in the body. 

* As a matter of fact a small part of the nitrogen is oxidized to nitric acid in 
the bomb calorimeter, but this is determined and its heat of formation subtracted, 
so that the final results are as stated above. 



142 



CHEMISTRY OF FOOD AND NUTRITION 



Heats of Combustion axd Approximate Elementary Composition of 
Typical Compounds 



Substance 


Heat OF 

COMBUS- 
TION 

Calories 

PER GRAM 


Carbon 

PER 
CENT 


Hydro- 
gen 

PER 

CENT 


Oxygen 

PER 

CENT 


Nitro- 
gen 

PER 

CENT 


Sul- 
phur 

PER 
CENT 


Phos- 
phorus 

PER 
CENT 


Glucose 


3-75 


40.0 


6.7 


53-3 








Sucrose 










3-96 


42.1 


6.4 


51-5 








Starch 
Glycogen J 










4.22 


44.4 


6.2 


49.4 








Body fat . 










9.60 


76.5 


12.0 


II. 5 








Butter fat 












9-30 


75-0 


II. 7 


133 








Edestin 












5-64 


514 


7.0 


22.1 


18.6 


0.9 




Legumin 












S.62 


51-7 


7.0 


22.9 


18.0 


0.4 




Gliadin 












5-74 


52.7 


6.9 


21.7 


17.7 


I.O 




Casein . 












5.85 


53-1 


7.0 


22.5 


15-8 


0.8 


0.8 


Albumin 












5.80 


52.5 


7.0 


23.0 


i6^o 


1-5 




Gelatin 












15-30 


50.0 


6.6 


24.8 


18.0 


0.6 




Creatinine 










4-58 


42.5 


6.2 


14.1 


37-2 






Urea . . 










2-53 


20.0 


6.7 


26.7 


46.6 









Since the energy used in the body is obtained from the oxi- 
dation of the same kinds of compounds which exist in food, 
i.e. from carbohydrates, fats, and proteins (or their cleavage 
products), we can estimate the amount of energy transformed in 
the body if we know the amount of each kind of foodstuff oxi- 
dized. Account must, however, be taken of the completeness 
of the oxidation in each case. 

When undergoing complete oxidation in the bomb calorimeter 
the foodstuffs yield the following average heats of combustion : 



Carbohydrates 

Fats 

Proteins 



4.1 Calories per gram. 
9.45 Calories per gram. 
5.65 Calories per gram. 



In the body carbohydrates and fats are oxidized to the same 
products as in the calorimeter and so yield the same amounts 
of heat. Protein, however, which burns in the bomb to carbon 
dioxide, water, and nitrogen, yields in the body no free nitrogen. 



THE FUEL VALUE OF FOOD 1 43 

but urea and other organic nitrogen compounds which are 
eliminated as end products. These organic nitrogenous end 
products are combustible ; they represent a less complete oxi- 
dation of protein in the body than takes place in the bomb. 
The loss of potential energy calculated on the assumption that 
all nitrogen left the body as urea would be about 0.9 Calorie 
per gram of protein, but on account of the elimination of other 
substances of higher heat of combustion (creatinine, uric acid, 
etc.), the actual loss in the form of combustible end products is 
considerably greater and averages about 1.3 Calories for each 
gram of protein broken down in the body. 

Hence, when the body burns material which it has previously 
absorbed, it obtains : 

From carbohydrates 4.1 Calories per gram. 

From fats 9.45 Calories per gram. 

From protein (5.65 — 1.30 = ) 4.35 Calories per gram. 

In calculating the fuel value of the food, however, allow- 
ance must be made for the fact that a part of each of the ma- 
terials is lost in digestion.* 

The approximate averages on a mixed diet are : 

Carbohydrates 2% lost, 98% absorbed. 
Fats s% lost, 95% absorbed. 

Protein 8% lost, 92% absorbed. 

The approximate physiological fuel values of the food constit- 
uents are then : 

Carbohydrates 4.1 X 98% = 4. Calories per gram. 
Fats 9.45 X 95% = 9. Calories per gram. 

Protein 4.35 X 92% =4. Calories per gram. 

The figures given by Rubner as representing the fuel values of food con- 
stituents are as follows : '"^ 
Carbohydrates 4 . i 
Fats 9.3 
Protein 4.1 

* The expression "lost in digestion " is here used in the sense explained in Chapter 
IV. 



r 



144 CHEMISTRY OF FOOD AND NUTRITION 

These were derived from experiments with dogs fed on meat, starch, 
sugar, etc., and therefore do not allow for so much loss in digestion as has 
been found to occur with men living on ordinary mixed diet. 

Fuel Value of Food Materials 

If the composition of a food is known, its approximate fuel 
value is easily computed by means of the above factors. Thus 
milk of about average composition contains : 

Protein, 3.3 per cent; fat, 4.0 per cent; carbohydrate, 5.0 
per cent. 
One hundred grams of such milk will furnish in the form of 
protein {t,.;^ X 4. =) 13.2 Calories; of fat (4.0 X 9. =) 36.0 
Calories; of carbohydrate (5.0 X 4. = ) 20.0 Calories; total 
for 100 grams of milk, 69.2 Calories. 

Eggs contain * on the average, in the edible portion, 13.4 
per cent protein, 10.5 per cent fat, and no appreciable amount 
of carbohydrate. They would then furnish per 100 grams 
(13.4 X 4) + (io-5 X 9) = 148. 1 Calories. 

Milk and eggs are sufficiently similar to be used interchange- 
ably in the adult dietary within reasonable Hmits, but evi- 
dently they furnish, weight for weight, very different amounts 
of nutrients and energy. Ordinarily the quantities to be 
taken as equivalent or mutually replaceable are those which 
furnish equal fuel value, e.g. loo-Calorie portions, the weights 
of which may be calculated directly from the fuel values of 100 
grams. 

Thus, for milk — 100 grams furnish 69.2 Calories; then, 
if X be the number of grams which furnish 100 Calories : 
100 : 69.2 ::x: 100 ; x = 145. f 

Similarly for eggs: 

100 : 148 :: X : 100 ; x = 68. 

* These and all similar statements of average composition are based on Bull. 
28, Office of Experiment Stations, U. S. Dept. Agriculture. 

t It is considered sufficiently accurate to state these quantities to the nearest 
whole number of grams. 



THE FUEL VALUE OF FOOD 



145 



And since the two extremes in the proportion are always the 
same, the weight in grams of the loo-Calorie portion may al- 
ways be found by dividing 10,000 (the product of the extremes) 
by the number of Calories per 100 grams. 

The fuel value of foods is often stated in Calories per pound. 
Thus in the same table (Bull. 28) from which the above figures 
for composition are taken, the fuel value of milk is given as 
325 Calories per pound. Since 453.6 grams furnish 325 Calo- 
ries, — 

453-6 : 325 : : -'^" : 100 1 x = 139.6, 

the number of grams required to furnish 100 Calories. This 
figure is about 3 per cent less than the one found above be- 
cause it is based on a fuel value computed by Rubner's factors, 
which are 2.5 to 3.3 per cent higher than the factors based on 
more recent work. (See above.) 

1^ The following figures for a few common food materials* 
are based upon the more recent factors, and show the weight of 
the loo-Calorie portion in grams and ounces, and the distribu- 
tion of the calories between proteins, fats, and carbohydrates: 

Table of ioo-Calorie Portions f of Food Material Based on the 
Factors — Protein, 4 ; Fat, 9 ; Carbohydrate, 4 



Food Material 
(Edible Portion) 



Weight of Portion 



Grams Ounces 



Distribution of Calories 



In protein In fat 



In carbo- 
hydrates 



Beef, free from visible fat 
Beef, round steak . . . 

Beef, corned 

Ham, lean 

Ham, fat 



64 
33 
37 
19 



3-0 

2-3 

1-3 
1.2 

0.7 



80.4 

54-5 
20.9 
29.7 
II. I 



19.6 

45-5 
79.1 

70-3 
88.9 



* Arranged according to the classification used in the bulletins of the U. S. 
Department of Agriculture and in Konig's well-known reference work Die Chemie 
der Menschlichen Nahrungs- und Genussmillel, viz. meats, fish, eggs, dairy products, 
grain products, sugars and starches, vegetables, fruits, nuts, oils. 

t Table i of Appendix B shows loo-Calorie portions of a much larger number of 
food materials. 



146 



CHEMISTRY OF FOOD AND NUTRITION 



Table of ioo-Calorie PoRTioNst of Food Material Based on the 
Factors — Protein, 4; Fat, 9; Carbohydrate, 4 {Continued) 



Food Material 
(Edible Portion) 



Bacon, smoked . . . 

Codfish 

Salmon 

Eggs 

Milk 

Butter 

Corn meal .... 

Oatmeal 

Rice 

Wheat, "entire" . . 
Wheat flour . . . . 
Bread, white . . . 

Sugar 

Asparagus . . . . 
Beans, dried . . . . 
Beans, string . . . 

Beets 

Cabbage 

Carrots 

Celery 

Corn, green or canned 

Lettuce 

Potatoes 

Spinach 

Tomatoes 

Turnips 

Apples 

Bananas 

Currants, dried . . , 
Oranges . . . . " , 
Peaches .... 
Pineapple .... 

Plums 

Prunes, dried . . 
Raisins .... 
Almonds .... 
Chestnuts . . . 
Peanuts .... 
Olive Oil .... 



Weight of Portion 



Grams Ounces 



16 
143 

49 

67 
145 

14 

27 

25 
28 
28 
28 
38 

25 

450 

29 

240 

216 

317 
220 

540 
99 
523 
120 
418 
438 
253 
159 

lOI 

31 

194 

242 

232 

118 

33 

29 

15 

43 

18 



0.6 
5-0 
1-7 
2-3 
51 
0-5 
i.o 
0.9 
1.0 
1.0 
1.0 

1-3 

0.9 

16.0 

1.0 

8.4 

7-4 
II. I 

7-7 

19.1 

3-2 

18.4 

4.2 

14.7 

15-5 

8.9 

5-6 

3-5 

1. 1 

6.8 

8.5 
8.2 

4-1 
1.2 
1.0 
0.5 
1-5 
0.6 
0.4 



Distribution of Calories 



In protein In fat 



6.7 
95-0 
43-3 
36.1 
19.0 

0.5 

9.0 

16.1 

9.1 

14-7 
11.8 
14.1 

32.4 
26.1 
22.2 
13-8 
20.3 
9-7 
23.8 
12.2 
25.2 
lo.s 
35-1 
iS-7 
13.2 

2-5 

S-2 

3-0 

6.2 

6.8 

3-7 

4-7 

2.8 

30 

13-0 

10.7 

18.8 



93-3 
5-0 
56.7 
639 
52.0 

99-5 

11.4 

16.2 

0.7 

3-5 
2.8 

4-5 

8.2 
4-7 
6.5 
2.0 
8.6 

7.9 

4.8 

9.8 

14.1 

1.2 

"•3 

15.7 

4.6 

7.2 

5-4 

4-7 

3-5 

2.2 

6.3 



8.6 
76.4 
16.6 
634 



In carlx)- 
hydrates 



29.0 

79.6 
67.7 
90.2 
81.8 
854 
81.4 
100. o 

594 
69.2 

713 
84.2 
71. 1 
82.4 
71.4 
78.0 
60.7 
88.3 
53-6 
68.6 
82.2 
90.3 
894 
92.3 
90-3 
91.0 
90.0 

95-3 
97.2 
88.4 
10.6 
72.7 
17.8 



THE FUEL VALUE OF FOOD 147 

Since proteins and carbohydrates have the same average 
fuel value and the ash of food does not as a rule constitute a 
large percentage, the striking differences in the weights of the 
various foods required to furnish 100 Calories are usually 
referable to differences in water content or fat content or both. 
That beans have nearly 20 times the fuel value of celery is 
essentially due to the difference in moisture, while the differ- 
ence in fuel value between lean beef and bacon, or between 
codfish and salmon, is chiefly a matter of fat content. Meat 
free from fat is about three fourths water and one fourth pro- 
tein, and so has a fuel value of about one Calorie per gram, while 
clear fat has a fuel value about nine times as great. 

Fuel values of meats as given in the standard tables are apt 
to be somewhat misleading, inasmuch as they allow for all the 
fat ordinarily found on the various cuts as taken from the 
animal, whereas in many cases a considerable part of this fat 
is trimmed off by the butcher and treated as a by-product; 
and often much of the remaining fat is removed either in the 
kitchen or at the table. If a pound of steak consists of 14 
ounces of clear lean, and 2 ounces of clear fat, and the fat is 
not eaten, at least half of the total fuel value of the pound of 
steak is lost. 

Many vegetables are more watery than lean meats and so 
contrast even more strikingly with the fats. An ounce of clear 
fat pork is equal in fuel value to about two pounds of cabbage ; 
an ounce of olive oil to over three pounds of lettuce. 

In connection with such comparisons of fuel value, however, 
it should be emphasized that the fuel value of a food, while of 
primary importance, is not alone a complete measure of its 
nutritive value, which will depend in part also upon the amounts 
and forms of nitrogen, phosphorus, iron, and various other 
essential elements furnished by the food. 

In order to indicate relative richness in nitrogenous constituents (pro- 
tein), it is not uncommon to state the "nutritive ratio" along with the fuel 



148 CHEMISTRY OF FOOD AND NUTRITION 

value of a food. The "nutritive ratio" or "nutrient ratio" is the ratio of 
non-nitrogenous to nitrogenous nutrients, compared on the basis of fuel 
values. Since the fuel values of carbohydrates and protein are taken as 
equal (4 Calories per gram), and that of fats as 2^ times as great (9 Calories 
per gram), the nutritive or nutrient ratio may be shown as follows : 

Carbohydrate + 2j Fat : Protein :: x : i ; 
or the ratio may be expressed in the form of a fraction : 

Carbohydrate + 2J Fat 
Protein 

These expressions can, of course, be appUed equally well to percentages or 
to weights of nutrients. 

The same information as is given by the statement of fuel value per pound 
and nutritive ratio may be obtained by comparing the weight of loo-Calorie 
portions and the percentages of calories supplied by protein as shown in the 
above table. The statement that 19 per cent of the calories of milk are 
furnished by protein is equivalent to giving the nutritive ratio of milk as 4.3. 



ENERGY REQUIREMENT IN METABOLISM — METHODS OF 
STUDY AND AMOUNTS REQUIRED FOR MAINTENANCE 
AT REST 

We know definitely from accurate experiments that the 
" physiological fuel values " which have been deduced repre- 
sent the energy which is actually obtained by the body from 
the food and which appears as muscular work or as heat; 
and we have every reason to suppose that under ordinary 
conditions the carbohydrates, fats, and proteins each supply 
the body with the kinds of energy needed for its maintenance 
and for its work, approximately in proportion to their fuel 
values as calculated above. We do not now believe that any 
one nutrient is used to the exclusion of others as a source of 
energy for any particular function, nor indeed that the body 
makes any particular distinction between the foodstuffs as 
sources of energy. The fuel value of the diet as a whole is 
utilized to meet the energy requirements of the whole body. 
For the present, therefore, it is the fuel value of the day's 



THE FUEL VALUE OF FOOD 149 

dietary which we have to consider rather than the distribution 
of this as regards protein, fats, and carbohydrates. 

The total food (or energy) requirement is best expressed in 
Calories per day, either for the whole body or per kilogram of 
body weight, and for convenience of discussion it is usually 
assumed that the average body weight (without clothing) is 
for men 70 kilograms (154 pounds) and for women eight tenths 
as much, 56 kilograms (123 pounds). 

There are four important methods of studying the food 
requirements of man : * 

1. By observing the amount of food consumed (dietary 
studies). 

2. By observing the amount of oxygen consumed — pref- 
erably also the respiratory quotient (respiration experiments). 

3. By determining the balance of intake and output (car- 
bon and nitrogen metabolism experiments). 

4. By direct measurement of heat given off by the body 
(calorimeter experiments). 

Dietary studies. — Most dietary studies give Httle more 
than a general indication of the food habits of the people 
studied ; but in cases where persons have maintained for a 
long time the same dietary habits and other conditions of life, 
and the body weight has remained practically constant, it 
may be fairly safe to assume that the food has furnished just 
about the right amount of energy for the maintenance of the 
body under the observed conditions. 

Great care must be taken in drawing inferences from the 
body weight because of the readiness with which the body 
gains or loses moisture. Athletes often lose 2 or 3 pounds in 
an hour of vigorous exercise and regain it in less than a day. 
Gain or loss of body weight during short periods, therefore, 

* For an account of the historical development of the principles which underUe 
the measuremetit of metabolism, see the introductory chapter of Lusk's Elements 
oj the ScietKe oj Nutrition. 



150 CHEMISTRY OK FOOD AND NUTRITION 

does not by any means necessarily imply a corresponding 
gain or loss of fat. The body may lose fat and at the same 
time maintain its weight through gaining water, or vice versa. 
When, however, the weight remains nearly the same for months 
at a time, it may usually be assumed that there is no impor- 
tant gain or loss of tissue and that the body is receiving just about 
the proper amount of total food for its needs. Under these 
conditions an accurate observation of the food consumed may 
give valuable indications as to the actual food requirement. 
Of such dietary studies perhaps the most useful individual ex- 
ample is that of Neumann, who reduced his diet to what ap- 
peared to be just about sufficient for his needs and then recorded 
all food and drink taken during a period of 10 months in which 
the body weight remained nearly constant. The average 
daily food furnished : * 



Nutrients Factors Calories 



Total Calories 
per Day 



Protein 66.1 grams X 4. = 264.4 

Fat 83.5 grams X 9. = 751.5^2242 

Carbohydrate t . ■ • 306.5 grams X 4. = 1226.0 

The 2242 Calories per day were evidently fully sufficient 
to meet the energy requirements of this man, whose weight 
was 66.5 to 67 kilograms (about 147 pounds) and who was en- 
gaged at his usual (mainly sedentary) professional work in the 
Hygienic Institute at Kiel. 

Later, when his weight had increased to 71.5 kilograms (157 
pounds) as the result of following for a time a more liberal 
diet (furnishing about 2600 Calories per day), he again observed 
his dietary while taking what was supposed to be an amount of 
food sufficient for the maintenance of the body and no more. 
This second dietary study was continued for 8 months, during 
which the average daily food consumption was found to be : 

* The data are taken from Chittenden's Nutrition of Man, page 2cS6. 
t Including some alcohol (taken in the form of beer), which is estimated as 
equivalent in fuel value to 1.75 times its weight of carbohydrates. 



THE FUEL VALUE OF FOOD 151 

Nutrients Factors Calories '^%\\%^°'''^^ 

Protein 76.2 grams X 4- = 304-8 

Fat 109.0 grains X 9. = 981.0 

Carbohydrates* . . . 178.6 grams X 4. = 714.4 

The body weight remained nearly constant. 

These results indicate that this subject, a man of average 
size, living a normal professional life involving no manual 
labor in the ordinary sense, but not excluding such muscular 
movements as are naturally incidental to a sedentary occupa- 
tion, found his energy requirements satisfied with food furnish- 
ing 2000 to 2250 Calories per day. 

Respiration experiments. — Since the foodstuffs yield their 
energy through being oxidized in the body, it is evident that a 
measure of the energy metabolism can be obtained by finding 
either the amount of foodstuffs oxidized or the amount of oxy- 
gen which is consumed in the process. The apparatus devised 
and used by Zuntz for this purpose provides a mask, fitting air- 
tight over the mouth and nose and connected by means of 
valved pipes with apparatus for measuring and analyzing the 
inspired and expired air. In this way one can determine the 
volume of oxygen entering, and the volume leaving, the lungs. 
The difference is the volume consumed in the body. 

Benedict has devised an improved form of respiration ap- 
paratus in which the subject breathes, either through a mouth- 
er nose-piece, from a current of air which is purified and kept 
in circulation in the same manner as that of the respiration 
calorimeter chamber described below. The carbon dioxide 
which the man produces is absorbed quantitatively and the 
oxygen which he consumes is exactly replaced by admitting 
measured volumes of analyzed oxygen gas from a cylinder of 
compressed oxygen, 

* Including some alcohol (taken in the form of beer), which is estimated as 
equivalent in fuel value to 1.75 times its weight of carbohydrates. 



152 



CHEMISTRY OF FOOD AND NUTRITION 



A given volume of oxygen used in the body may liberate 
somewhat different amounts of heat, according as it oxidizes 
fat, carbohydrate, or protein. For accurate estimations of 
the energy liberated it is therefore necessary to know the kind 

Spirometer 



Lungs 




0. 



Pump 



Absorbed 



Absorbed 



Fig. 7. 



Diagram of Benedict respiration apparatus. 
Benedict. 



Courtesy of Dr. F. G. 



of material oxidized, as well as the amount of oxygen con- 
sumed. This is calculated from the respiratory quotient. 

Since the amount of protein broken down in the body can 
be estimated from the nitrogen excretion, the determination of 
the respiratory quotient along with the o.xygen consumption 
shows the extent of the combustion in the body and the pro- 



THE FUEL VALUE OF FOOD 



153 



portions of fat and carbohydrate burned.* From these data 
the energy can be calculated. 

As a matter of fact it is not necessary to go through the 
actual calculation of the amounts of fat and carbohydrate 
burned since the energy derived from a Hter of oxygen when 
used to burn carbohydrate and fat in different proportions 
can be calculated once for all and expressed in relation to the 
respiratory quotient as shown in the accompanying table. 

Energy Values of Oxygen and Carbon Dioxide at Different 
Respiratory Quotients (Zuntz and Schumberg) 



Respiratory 
Quotient 


Calories 

PER Liter of 

Oxygen 


Calories 

PER Liter of 

Carbon Dioxide 


Calories 

PER Gram of 

Carbon Dioxide 


0.70 


4.686 


6.694 


3.408 


0.71 


4.690 


6.606 


3-363 


0.72 


4.702 


6.531 


3.325 


0.73 


4.714 


6.458 


3.288 


0.74 


4.727 


6.388 


3.252 


0.7S 


4-739 


6.319 


3.217 


0.76 


4-752 


6-253 


3.183 


0.77 


4.764 


6.187 


3.150 


0.78 - 


4.776 


6.123 


3.117 


0.79 


4.789 


6.062 


3.086 


0.80 


4.801 


6.001 


3.055 


0.81 


4.813 


S-942 


3.025 


0.82 


4.82s 


5.884 


2.996 


0.83 


4-838 


5.829 


2.967 


0.84 


4.850 


S-774 


2-939 


0.85 


4.863 


S-72I 


2.912 


0.86 


4.87s 


5.669 


2.886 


0.87 


4-887 


5-617 


2.860 


0.88 


4.900 


S.568 


2.835 


0.89 


4.912 


5.519 


2.810 



* Or, with very little error, it may be assumed that 15 per cent of the oxygen 
goes to bum protein and the rest is divided between fat and carbohydrate. The 
values given in the table herewith agree with this assumption. Attention should 
be called to the fact that estimates of energy metaboUsm based on carbon dioxide 
production alone involve larger errors than those based on oxygen consumption 
alone. 



154 



CHEMISTRY OF FOOD AND NUTRITION 



Energy Values of Oxygen and Carbon Dioxide at Different 
Respiratory Quotients (Zuntz and Schumberg) (Continued) 



Respiratory 
Quotient 


Calories 


Calories 


Calories 


PER Liter of 


PER Liter of 


PER Gram of 


Oxygen 


Carbon Dioxide 


Carbon Dioxide 


0.90 


4.924 


5-471 


2.78s 


0.91 


4-936 


5-424 


2.761 


0.92 


4.948 


5-3/8 


2-738 


0.93 


4.960 


5-333 


2-715 


0.94 


4-973 


5.290 


2.693 


0.95 


4-985 


5-247 


2.671 


0.96 


4-997 


5-205 


2.650 


0.97 


5.010 


5-165 


2.629 


0.98 


5.022 


5.124 


2.609 


0.99 


5 -034 


5-085 


2.589 


1. 00 


5-047 


S-047 


2.569 



It is then only necessary to determine the respiratory quotient 
and the volume of oxygen used in order to know the number 
of Calories of energy metabolized. This is sometimes called 
the method of indirect calorimetry. 

This method of studying the total metabolism permits of 
experiments being carried out very quickly, and is therefore 
especially useful for the direct investigation of conditions which 
affect metabolism promptly, such as muscular work or the 
eating of food. The periods of observation cannot be very long, 
but the probable results for the 24 hours' metaboUsm can be 
estimated by the data obtained during frequent short periods 
at different times of the day and night. For a critical com- 
parison of this method with the Pettenkofer and Voit method 
of studying metabolism by the determination of the carbon 
balance, the reader is referred to the discussion by Magnus- 
Levy in Von Noorden's Metabolism and Practical Medicine, 
Vol. I, pages 186-198. 

From the results of many observations by the Zuntz method 
Magnus-Levy estimates the minimum metabolism of a man 
of average size kept absolutely motionless and fasting at 1625 



THE FUEL VALUE OF FOOD 155 

Calories per day. Food barely sufficient for maintenance would 
increase this by 175, and such incidental muscular movements 
as would ordinarily be made by a man at rest in bed would in- 
volve another 200, making a total of 20CK) Calories as the esti- 
mated food requirement of a man at rest with a maintenance diet. 
Magnus-Levy further estimates that the man, if doing no work 
(in the ordinary sense), but allowed to move about the room in- 
stead of remaining in bed, would require 2230 Calories per day. 

Carbon and nitrogen balance experiments. — From a com- 
parison of the constituents of the food consumed (" intake ") 
and of the substances eliminated from the body (" output "), 
the material actually oxidized and the energy liberated in the 
oxidation may be determined. 

The intake is found by weighing and analyzing all food 
eaten; the output by collecting and determining the end 
products eliminated through the lungs, the kidneys, the intes- 
tines, and sometimes (in very exact experiments) the skin. The 
time unit in experiments upon the intake and output is almost 
always 24 hours, the experimental day beginning preferably just 
before breakfast. The feces belonging to the experimental days 
are marked, usually by giving a small amount of lampblack with 
the food as in ordinary digestion experiments, separated and 
analyzed. The end products given off by the lungs and kidneys 
during an experimental day are taken as measuring the material 
broken down in the body during the same period. 

Some time is of course required for the elimination of the 
nitrogenous end products through the kidneys. This un- 
avoidable " lag " in the eHmination of nitrogen may intro- 
duce an error in determining the nitrogen balance unless the 
subject has been kept for a few days in advance upon the 
same diet which is to be used in the experiment. 

Assuming that the total nitrogen and carbon of the ab- 
sorbed food existed in the form of protein, fat, and carbo- 
hydrate, and that the amount of carbohydrates in the body is 



iS6 



CHEMISTRY OF FOOD AND NUTRITION 



constant from day to day, it is only necessary to determine the 
carbon dioxide of the expired air and the carbon and nitrogen 
of the waste products, in order to calculate the amounts of 
material oxidized and of energy liberated in the body. Ex- 
periments of this sort have played a most important part in 
the development of our knowledge of nutrition. The cal- 
culations are usually based on the following average analyses 
of protein and body fat: 

Fat 



Carbon 
Nitrogen 
Hydrogen 
Oxygen . 
Sulphur 




76.5 

12 
"•5 



The following data were obtained with a man on ordinary 
mixed diet : 

Calculation of Energy Metabolism from Carbon and Nitrogen 
Balance. Max of 64 Kilograjis at Rest in Atwater Respiration 
Apparatus, 





Grams per Day 


Intake 


Protein 


Fat 


Carbo- 
hydrate 


Nitrogen 


Carbon 


Total in food . . . 

Lost in digestion 
Absorbed .... 


94.4 

5-4 
89.0 


82.5 

3-7 

78.8 


289.8 

3-2 

286.6 


151 

0.9 



14.2 

16.2 

16.2 

— 2.0 


239.0 

7-4 
231.6 


Output 




Bj' lungs 


207.3 
12.2 


B}'' kidneys 


Metabolized 


219-5 
+ 12. 1 


Balance 







THE FUEL VALUE OF FOOD 157 

A loss of 2.0 grams body nitrogen indicates (2.0 X 6.25 =) 
12.5 grams body protein burned. Also there were 89.0 grams 
absorbed from food, and, therefore, in all 101.5 grams total 
protein burned. 

Since the respiratory quotient showed that the body was 
in carbohydrate equilibrium at the beginning and end of each 
experimental day, i.e. at seven o'clock each morning, it may 
be concluded that the amount of carbohydrate burned was 
the same as that absorbed from the food, viz. 286.6 grams 
per day. 

From the carbon balance, therefore, we estimate the amount 
of fat burned as follows : 

12.5 grams body protein yield (12.5 X 53 per 

cent = ) 6.6 grams carbon 

and there were in the absorbed food . . . . 231.6 grams carbon 

.'. total available was 238.2 grams carbon 

But total catabolized was only 219.5 grams carbon 

.'. the body stored in the form of fat 18.7 grams carbon 

Since fat contains 76.5 per cent carbon, i gram carbon =0= 1.307 grams 
fat. .*. 18.7 grams carbon = 24.4 grams fat. 

The body therefore absorbed 78.8 grams fat 
stored 24.4 grams fat 
burned 54.4 grams fat 

In all the body burned per day 

101.5 grams protein, yielding (101.5 X 4.35 * = ) 442 Calories 
54.4 grams fat, yielding (54-4 X 9.45 * = ) 515 Calories 

286.6 grams carbohydrate, yield- 
ing (286.6 X 4.1 * = ) 1 1 75 Calories 

2132 Calories 

By means of the carbon and nitrogen balance Sonden and 
Tigerstedt studied the energy metaboHsm of eight resting men 
between nineteen and forty-four years of age, with results which 
varied for the different subjects from 1853 to 2292 Calories 

* Here the factors for fuel value are not reduced to allow for loss in digestion, 
because this loss has already been deducted in computing the amount of each 
nutrient actually absorbed and rendered available. 



158 CHEMISTRY OF FOOD AND NUTRITION 

per day. Many other experimenters have used the same method 
with similar results. 

Calorimeter experiments. — The most direct, and in some 
respects most convincing, way of ascertaining the energy me- 
tabolism is by the method oj direct calorinietry. This consists in 
measuring the total energy expenditure of the body as heat or 
as heat and mechanical work by confining the subject in a 
chamber permitting of actual measurement of the heat produced. 
It was not until the development of the Atwater-Rosa- 
Benedict respiration calorimeter that complete and satisfactory 
data covering periods of one to several days were obtained. 
This apparatus consisted of an air-tight copper chamber, sur- 
rounded by zinc and wooden walls with air-spaces between, 
and was large enough for a man to live in without discomfort, 
being about 7 feet long, 4 feet wide, and 6^ feet high. An 
opening in the front of the apparatus, which was sealed during 
an experiment, serves as both door and window and admits suf- 
ficient light for reading and writing. A smaller opening, having 
tightly fitting caps on both ends, was used for passing food, drink, 
excreta, etc., into and out of the chamber. The chamber 
was furnished with a folding bed, chair, and table, and was 
ventilated by means of a current of air which passed usually at 
the rate of about 2^ cubic feet per minute. At first this venti- 
lating air current was maintained and measured by means of a 
specially constructed meter pump which also automatically 
took samples of the air for analysis. Later the apparatus 
was so modified as to make use of the same air throughout an 
experiment, the carbon dioxide and water given off by the sub- 
ject being removed by circulating the air through purif>ang 
vessels, and the oxygen which the subject uses being replaced 
by adding weighed amounts of oxygen to the air current as 
required.* By this means it is possible to carry out, in the 

* Figure 8 indicates diagrammatically the ventilating system as applied in one 
of the later forms of apparatus. 



THE FUEL VALUE OF FOOD 



159 



^ \ \ \ \ 



O TENSION 
EQUALIZER 



2J' 



0, INTRODUCED" 



yy 




vv 



r^ 



H2O 
ABSORBED 



H,S 0, 



CO, 
ABSORBED 

POTASH 

LIME 



H^O 
ABSORBED 



H2S O4 



BLOWER 



Fig. 8. — Diagram of ventilation of respiration calorimeter. The air is taken 
out at lower right-hand corner and forced b> the blower through the apparatus for 
absorbing water and carbon dioxide. It returns to the calorimeter at the top. 
O.xj-gen can be introduced into the chamber itself as need is shown by the tension 
equalizer. Courtesy of Dr. F. G. Benedict and the Carnegie Institution of 
Washington. 



l6o CHEMISTRY OF FOOD AND NUTRITION 

calorimeter, metabolism experiments in which the oxygen and 
hydrogen as well as the carbon and nitrogen balances are 
determined, and from these .data the gain or loss of carbohy- 
drate as well as of protein and fat can be determined. 

The ventilating air current is so regulated that it enters 
and leaves the calorimeter at the same temperature; and 
between the copper and zinc walls are placed a large number 
of thermo-electric junctions connected with a deHcate gal- 
vanometer by means of which each wall is tested every four 
minutes, day and night, during the progress of an experiment, 
and the minute amounts of heat which may pass to or from 
the calorimeter through its walls are quickly detected and 
made to balance each other. Thus there is no gain or loss of 
heat either through the walls of the chamber or by the venti- 
lating air current, and the heat given off by the subject can 
leave only by the means especially provided for carrying it 
out and measuring it. A part of the heat Uberated is carried 
from the chamber in latent form by the water vapor in the 
outgoing air, which is accurately determined. The rest of 
the heat is brought away by means of a current of cold 
water circulating through a copper pipe coiled near the ceiling 
of the chamber. The quantity of water which passes through 
the pipe and the difference between the temperature at which 
it enters and that at which it leaves the coil are carefully 
determined and show how much heat is thus brought out of 
the chamber. 

In recent years several different calorimeters, based on the 
principles of the apparatus just described but adapted in size 
and shape to different types of experimentation, have come into 
use. Notable among these are the " chair " and the " bed " 
calorimeters, which are so constructed as to accommodate a 
subject in the sitting or reclining position in comfort but 
in a minimum of space; for only by making the calorimeter 
chamber small is it practicable to obtain a high degree of 



THE FUEL VALUE OF FOOD 



i6i 



<z^ 




.b 2 



1 62 CHEMISTRY OF FOOD' \XD NUTRITION 

accuracy in experiments of a few hours' duration. Figures g, 
lo, and II show sectional diagrams of the original calorimeter 
chamber and of the more recent chair and bed calorimeters 
respectively. 

Detailed and illustrated descriptions of the chief forms of 
apparatus now in use may be found in the pubUcations by Bene- 
dict and Carpenter, by Langworthy and Milner, and by Lusk, 
Riche, and Soderstrom, full references to which are given at the 
end of this chapter. 

By means of the Atwater-Rosa-Benedict apparatus and its 
various modifications, it has been possible to measure the heat 
production or energy expenditure of a man for a day or for a 
period of days very accurately. In the original Atwater-Bene- 
dict series it was found that the difference in results determined 
by direct and indirect calorimetry was rarely as much as 2 
per cent, and in the average of 45 experiments covering a total 
of 143 days the difference was only o.oi per cent. The results 
obtained by direct energy measurements are therefore the 
same as those computed from respiration and metabolism ex- 
periments when the technique is of the best and the experiments 
are sufficiently prolonged. This agreement is in general less 
exact in individual experiments in proportion as the experi- 
mental periods are shortened; but the methods are now so 
highly developed that the results of direct and indirect calo- 
rimetry are considered practically interchangeable even for 
experiments of a few hours' duration. In 1913 Armsby com- 
piled the following summary of experiments both upon men, 
dogs, and cattle which had been published up to that time. It 
will be seen that the difference between the total heat produc- 
tion as computed and as directly measured is only one fourth 
of one per cent, or quite within the limits of accuracy of ex- 
perimental methods of this sort. 




Scale ; I Meter. 



Fig. lo. — Horizontal cross-section of chair calorimeter, showing cross-section of 
copper wall at A , zinc wall at B, hair-felt at E, and asbestos outer wall at F ; also 
cross-section of all upright channels in the steel construction. At the right is the 
location of the ingoing and outgoing water and the thermometers. iVt C is shown 
the food aperture, and Z? is a gasket separating the two parts. The ingoing and 
outcoming air-pipes are shown at the right inside the copper wall. The telephone 
is shown at the left, and in the center of the drawing is the chair with its foot-rest, G. 
In dotted line is shown the opening where the man enters. Courtesy of Dr. F. G. 
Benedict and the Carnegie Institution of Wasliington. 



164 



CHEMISTRY OF FOOD AND NUTRITION 



ExFERIlfENTER 


Total 
Number 

OF 

Days 


Total 
Computed 

Heat 

Production 

Calories 


Total Observed 
Heat 

Production 
Calories 


Percentage 
Difference 


Rubner 

Laulanie 

Atwater and Benedict . 
Benedict and Milnjr 

Benedict 

Armsby and Fries . . 


45 
7 
93 
24 
53 
114 


17,406 

1,865 

249,063 

95,075 
102,078 
976,204 


17,350 

1,859 

248,930 

95,689 
101,336 
980,234 


-0.32 

- 0.31 

— 0.05 
+ 0.65 

-0.73 
+ 0.41 




336 


1,441,691 


1,445,398 


+ 0.26 



As Armsby points out : " These results may be taken as dem- 
onstrating that the animal heat arises exclusively from the 
combustions in the body, but they have a much broader sig- 
nificance. They show that the transformations of chemical 
energy into heat and work in the animal body take place ac- 
cording to the same general laws and with the same equivalencies 
as in our artificial motors and in lifeless matter generally. 
The great law of the conservation of energy rules in the 
animal mechanism, whether in man, carnivora, or herbivora, 
just as in the engine. The body neither manufactures nor 
destroys energy. All that it gives out it gets from its food, 
and all that is supplied in its food is sooner or later recovered 
in some form." 

Since the time of Armsby's compilation the agreement be- 
tween the observed and computed heat production has been 
confirmed in many additional experiments, and both by the 
same and different experimenters. 

Working with the original Atwater calorimeter, Atwater and 
Benedict conducted " rest " experiments upon six different 
men who lived in the calorimeter as quietly as was feasible for 
days at a time, taking as a rule but little more exercise than 
was involved in dressing and undressing, folding and unfolding 



THE FUEL VALUE OF FOOD 



165 



the bed, table, and chair, taking samples and observations 
pertaining to the experiment, writing, etc., in short, the life of 
a healthy man, conlined to one small room. 

The average daily metabolism of each of the subjects was as 
follows : 



Subject 


Age 
Years 


Weight 
Average 


Number of 
Experi- 
ments 


Total Ex- 
perimental 
Days 


Calories 
PER Day 


E. 

A. W. S 

J. F. S 

J. C. W 

H. F 

B. F. D 

Mean of individual 
averages . . 


31-34 
22-25 

29 

SI 

54 
23 


70 K. 

(154 lb.) 

70 K. 
(154 lb.) 

65 K. 
(143 lb.) 

76 K. 
(168 lb.) 

70 K. 
(154 lb.) 

67 K. 
(147 lb.) 


13 
4 
4 

I 
I 
I 


42 

• 9 

12 

4 
3 
3 


2283 
2337 
2133 
2397 
1904 
2228 


2213 













Extreme deviations from the mean, + 184 to — 309 Calories, 

or + 8.4 to — 14 per cent. 

Omitting the results obtained with the one subject who 
was considerably older than the others, the figures become as 
follows : 

Mean of individual averages, 2277 Calories. 
Extreme deviations from mean, + 120 to — 144. Calories, 
or + 5.2 to — 6.3 per cent. 

Deviations in body weight, + 8.7 to — 7.1 per cent. 

The subject " H. F.," aged fifty-four, who believed that 
he consumed only half the usual amount of food, had a food 
requirement about 15 per cent less than that of the younger 



l66 CHEMISTRY OF FOOD AND NUTRITION 

men averaging about the same weight. The five younger men 
varied in age from twenty-one to thirty-four years, were natives 
of three different countries, and had been accustomed to very 
different dietary habits and modes of life, yet they differed less 
in energy requirements than in body weight. 

Summary of the Evidence Obtained by the Different Methods 

A general view of the results obtained by all four of the 
methods described shows them to be strikingly consistent and 
leads to the conclusion that the food rccjuirements of a young 
to middle-aged man of average size, without muscular work, 
eating a mixed diet sufficient to meet his need, approximates 
2000 Calories per day, and that such muscular activity as is 
incidental to very quiet living indoors may be expected to raise 
this requirement to about 2200 Calories per day. 

Lusk summarizes the mean energy requirement of an average 
sized man in somewhat more precise terms as follows : 

Absolute rest in bed without food 1680 Calories 

Absolute rest in bed with food 1840 Calories 

Rest in bed, 8 hours, sitting in chair 16 hours, 

with food 2168 Calories 

The very close agreement in results reached by many inde- 
pendent investigators, using four distinct methods of study, 
must be taken as estabhshing the approximate average food 
requirement of a man at rest beyond any reasonable doubt. 

Significance of Basal Energy Metabolism 

On account of the great importance of the fundamental 
energy expenditure both for the study of normal nutrition, 
and as a basis for comparison in the investigation of disease, 
the experiments above described have been followed by others 



THE FUEL VALUE OF FOOD 



167 



designed to establish with even greater exactness the " basal 
metabolism " which goes on when the direct effect of food is 
excluded and when muscular activity is suppressed as com- 




pletely as possible. Experiments of this latter type must neces- 
sarily be carried out in shorter periods than were used in the 
Atwater investigations described above. Being shorter, they 



1 68 CHEMISTRY OF FOOD AND NUTRITION 

can be more frequently repeated and more readily extended to 
cover a larger number of individuals. 

Data obtained in such studies of " basal metabolism " will 
be cited later in connection with the study of the various con- 
ditions which influence the energy metaboHsm and total food 
requirement. 

A systematic analysis of the maintenance requirement of 
the body with reference to its principal functions has not yet 
been made, but results obtained by Armsby, Atwater, Benedict, 
Lusk, Magnus-Levy, Rubner, Zuntz, and others indicate that 
in the healthy adult the expenditure of energy when at rest 
and no longer influenced by the direct effect of food (" basal 
energy metabolism ") may be attributed in part, perhaps up 
to one tenth, to the work of the heart in maintaining the cir- 
culation ; from one tenth to two tenths to the muscular work 
of respiration ; from one third to one half, or perhaps even more, 
to the maintenance of muscular tonus (tone, tension, elasticity) ; 
and an unknown fraction to other forms of internal work. 

REFERENCES 

Armsby. Principles of Animal Nutrition, Chapters 7 to 10. 

Armsby. Food as Body Fuel. Pennsylvania Agricultural Experiment 
Station, Bulletin 126. 

Atwater. Methods and Results of Investigations on the Chemistry and 
Economy of Food. Bull. 21, Office of E.xperiment Stations, U. S. 
Dept. Agriculture (1895). 

Atwater. Neue Versuche uber Stoff- und Kraft-wechsel. Ergebnisse 
der Physiologie, Vol. 3 (1904). 

Atwater and Benedict. A Respiration Calorimeter with Appliances 
for the Direct Determination of Oxj'gen. Publication No. 42, Car- 
negie Institution of Washington (1905). 

Atwater and Snell. A Bomb Calorimeter and Method of its Use. Jour- 
nal of the American Chemical Society, Vol. 25, page 659 (1903). 

Benedict. An Apparatus for Studying the Respiratory E.xchange. Amer- 
ican Journal of Physiology, Vol. 24, pages 345-374 (1909). 

Benedict and Carpenter. Respiration Calorimeters for Studying the 



THE FUEL VALUE OF FOCD 1 69 

Respiratory Exchange and Energy Transformations in Man. Car- 
negie Institution of Washington, Publication No. 123. 

CARPENTER. A Comparison of Methods for Determining the Respiratory 
E.xchange of Man. Carnegie Institution of Washington, Publication 
No. 216. 

Langworthy and Milner. An Improved Respiration Calorimeter for 
Use in Experiments with Man. Journal of Agricultural Research, 
Vol. 5, page 299. 

LtrSK. Elements of the Science of Nutrition. 

LusK, RiCHE, AXD SoDERSTROM. A Respiration Calorimeter for the Study 
of Disease. Archives of Internal Medicine, Vol. 15, pa^es 793, 805. 

Mathews. Physiological Chemistry, Chapter VI. 

RuBNER. Die Gesetze der Energieverbrauch bei dor Ernahrung. 

Von Noorden. Metabolism and Practical Medicine. 



CHAPTER VII 

CONDITIONS GOVERNING ENERGY METABOLISM 
AND TOTAL FOOD REQUIREMENT 

Activity, age, and size are the most important factors af- 
fecting the total food requirement of the body, but several 
other conditions, such as bodily constitution and environment, 
may have measurable influence. Since the food requirement of 
the adult is more accurately known than that of the growing 
organism, it will be best to consider the conditions affecting 
the energy metabolism of the adult first and the demands of 
growth later. 

Basal Metabolism of the Adult 

The basal rate of energy metabolism, as shown by the heat 
production (determined either by direct or indirect calorimetry) 
at complete rest and at a sufficiently long time after the last 
meal to eliminate the direct effects of food, has now been studied 
in considerable detail. In the healthy adult this basal metab- 
olism depends chiefly upon the size, shape, and composition of 
the body and the activity of certain internal processes. It 
may or may not be appreciably influenced by the temperature 
of the surroundings. 

Influence of the size, shape, and composition of the body. — 
For different adults of the same species the energy metaboHsm 
and therefore the total food requirement as a rule increases 
with the size, but not to the same extent that the body weight 
increases ; so that the requirement, though greater in absolute 

170 



CONDITIONS GOVERNING ENERGY METABOLISM 171 

amount, is less per unit of body weight in the larger individual 
than in the smaller. The energy metabolism increases in pro- 
portion to the surface rather than the weight. Thus, Rubner 
collected the following data from experiments upon seven dif- 
ferent dogs, all full grown but differing greatly in size. 





Body Weight 
Kilograms 


Heat Production in Calories per Day 


No. 


Total 


Per kilogram of 
body weight 


Per square meter 
of body surface 


I 

II 

III 

IV 

V 

VI 

VII 


3.10 
6.44 

9-51 
17.70 
19.20 

23-71 
30.66 


273.6 

417-3 
619.7 

817-7 

880.7 

970.0 

1 1 24.0 


88.25 
64.79 
65.16 • 
46.20 

45-87 
40.91 
36.66 


1214 
II 20 
1183 
1097 
1207 
III2 
1046 



Here the heat production in calories per kilogram was over 
twice as great in the smallest as in the largest dog, but the total 
metabolism was nearly proportional to the surface area through- 
out. 

That the relationship of energy metabolism to body surface 
is not due simply to loss of heat through the cooling effect of 
the environment will be apparent from the observations upon 
the regulation of body temperature. 

Armsby, in his Principles of Animal Nutrition, quotes the 
explanation offered by von Hosslin — that the internal work 
and the consequent heat production in the body are substantially 
proportional to the two thirds power of its volume, and since 
the external surface bears the same ratio to the volume, a 
proportionality necessarily exists between heat production and 
surface. 

Largely as the result of Rubner's work, it became customary 
to express energy requirements in terms of surface ; but, on 



172 CHEMISTRY OF TOOD AND NUTRITION 

account of the difficulties involved in actual measurements, 
the surface was customarily computed from the weight, usually 
by Meeh's formula S = W3XC or 5 = 12. 3V 1^2^ ir, vvhich S 
represents the surface and W the weight, the constant 12.3 
having been found by Meeh in a series of measurements of 
men. 

Benedict found that the basal metabolism of normal men 
and women per unit of surface as computed from the weight by 
the Meeh formula is by no means constant, varying from 29 to 
40 Calories per square meter per hour among 89 men, and 
from 26 to 38 Calories per square meter per hour among 68 
women. 

Recently DuBois and DuBois have made a new series of 
measurements of body surface in which they find that Meeh's 
formula gives results which are much too high, probably because 
Meeh's measurements were made on thin men. Tabulating 
the results of other measurements with their own, they find 
that among the 20 cases of direct measurements of body surface 
which had been reported up to 191 5, the errors in results com- 
puted by Meeh's formula range from —7 to +36 per cent. 
Differently stated, if the principle of Meeh's formula be em- 
ployed it would be necessary to vary the " constant " from 9.06 
to 13.17 in order to express the relationships of weight and 
surface actually found among these 20 individuals. 

The errors involved in computing the surface from the weight 
alone are therefore much greater than were formerly sup- 
posed. DuBois and DuBois have devised two new methods 
by which the surface may be computed with much greater ac- 
curacy : (i) from a series of nineteen measurements of differ- 
ent parts of the body, the surface of each part being computed 
and the results added together (" linear formula "), and (2) a 
" height-weight formula " which these authors have derived 
mathematically from the data of all available measurements of 
height, weight, and surface. 



CONDITIONS GOVERNING ENERGY METABOLISM 1 73 



The height-weight formula may be written thus : 

^4=iy0.425xi70.725xC 

or in the form : 

Log A = (Log WX 0.425) + (Log H X 0.725) + 1.8564 
in either of which 

A = Surface area in square centimeters 

H = Height in centimeters 

W = Weight in kilograms 

C = A constant (71.84) 

In connection with this formula the authors give also a chart * 
from which the approximate surface area may be obtained at 
a glance if height and weight are known. The "data given in 
the accompanying table have been taken from the DuBois 
chart. 

Table Showing Surface Area in Square Meters for Different 
Heights and Weights according to the Height-Weight Formula 
OF DuBois AND DuBois 





Height 




Weight in Kilograms 








METERS 


25 


30 


35 


40 


45 


50 


55 


60 


65 


70 


75 


80 


85 


90 


95 


100 


105 


200 














1.84 


1.91 


1.97 


2.03 


2.09 


2. IS 


2.21 


2.26 


2.31 


2.36 


2..41 


I9S 












1-73 


1.80 




87 




93 




99 


2 


05 


2. II 


2.17 


2.22 


2.27 


2.32 


2.37 


190 








1.56 


1.63 


1.70 


1-77 




84 




90 




96 


2 


02 


2.08 


2.13 


2.18 


2.23 


2.28 


2.3,3 


i8s 








1-53 


1.60 


1.67 


1.74 




80 




86 




92 




98 


2.04 


2.09 


2.14 


2.19 


2.24 


2.29 


180 








1.49 


1-57 


1.64 


1. 71 




77 




83 




89 




95 


2.00 


2.05 


2.10 


2.15 


2.20 


2.25 


175 


1. 19 


1.28 


1.36 


1.46 


1-53 


1.60 


1.67 




73 




79 




85 




91 


1.96 


2.01 


2.06 


2. II 


2.16 


2.21 


170 


1. 17 


1.26 


1-34 


1-43 


1.50 


1-57 


1.63 




69 




75 




81 




86 


1.91 


1.96 


2.01 


2.06 


2. II 




165 


1. 14 


1.23 


I-3I 


1.40 


1.47 


1-54 


1.60 




66 




72 




78 




83 


1.88 


1-93 


1.98 


2.03 


2.07 




160 


1. 12 


1. 21 


1.29 


1-37 


1.44 


1.50 


1.56 




62 




68 




73 




78 


1.83 


1.88 


1-93 


1.98 






155 


1.09 


I.I« 


1.26 


1-33 


1.40 


1.46 


1-52 




58 




64 




69 




74 


1-79 


1.84 


1.89 








ISO 


1.06 


115 


1.23 


1.30 


1.36 


1.42 


1.48 




54 




60 




65 




70 


1-75 


1.80 










145 


1.03 


1. 12 


1.20 


1.27 


1-33 


1-39 


1-45 




51 




56 




61 




66 


1. 71 












140 


1. 00 


1.09 


1. 17 


1.24 


1.30 


1.36 


1.42 




47 




52 




57 
















13s 


3.97 


1.06 


1. 14 


1.20 


1.26 


1-32 


1.38 




43 




48 


















130 


3.95 


1.04 


I. II 


1. 17 


1-23 


1.29 


1-35 




40 




















125 


3-93 


1. 01 


1.08 


1. 14 


1.20 


1.26 


I-3I 




36 




















120 


D.9I 


0.98 


1.04 


1. 10 


1. 16 


1.22 


1.27 























* Reproduction of the chart may be found on page 126 of the third edition of 
Lusk's Science of Nutrition. 



174 CHEMISTRY OF FOOD AND NUTRITION 

On applying the " height-weight formula " to the recorded 
energy metabolism of the large number of men studied in Bene- 
dict's laboratory, as well as in his own, DuBois finds that all 
the data for men under 50 years of age are within 15 per cent 
of the average basal heat production of 39.7 Calories per hour 
per square meter of surface area properly computed, and that 
86 per cent of all the cases are within 10 per cent of the average. 
Means, using the more accurate " Hnear formula," finds all of 
his 16 normal cases (9 men and 7 women) and also most of his 
obesity cases to fall within DuBois' " normal limits " {i.e. 
within 10 per cent of DuBois' average of 39.7 Calories per square 
meter per hour). DuBois ^ believes that one may " feel cer- 
tain that with men between the ages of 20 and 50 the (basal) 
metabolism of each individual is proportional to his surface 
area whether he be short or tall, fat or thin." 

Differences of build (shape of body) are associated not only 
with varying ratios of weight to surface but also with differ- 
ences of fatness, i.e. of body composition. The thin man, be- 
sides having a greater surface in proportion to his weight, 
differs also from the stout man in that a larger percentage of his 
body is actual protoplasm. Since the metabolism of the body 
depends more upon its weight of protoplasm (active tissue) than 
upon its total weight, we have here an important reason for 
believing that the food requirement will be greater in a tall, 
thin man than in a shorter and fatter man of the same weight. 

Von Noorden tested this question by observing the metab- 
olism (for one day without food) of two men of different build 
but nearly the same weight. The results were as follows: 
ist man, thin and muscular, weight 71. i kilograms — 2392 
Calories = 33.6 Calories per kilogram ; 2d man, stout, weight 
73.6 kilograms — 2136 Calories = 29.0 Calories per kilogram. 
These two men had nearly the same weight but differed in 
height, in body composition, and in energy expenditure. 

' AmcricdH Journal of the Medic jI Sciences, June, igi6, page 786. 



CONDITIONS GOVERNING ENERGY METABOLISM 175 

Even with the same height and weight there may be differ- 
ences in the composition of the body. Thus a man of average 
height and weight but large-boned and loosely built will be of 
less than average fatness; a man of the same height but less 
broad-shouldered must be somewhat fatter in order to weigh 
the same. Hence equality of height and weight does not neces- 
sarily imply the same shape and composition of body. Bene- 
dict finds among normal adults of like height and weight the 
basal metaboUsm of athletes about five per cent higher, and 
that of women about five per cent lower, than that of average 
non-athletic men. He attributes these divergencies to differ- 
ences in body composition, holding that women have some- 
what more fat, and athletes somewhat less, than non-athletic 
men of the same weight and height. 

Internal activities. — The work of maintaining the respiration 
and circulation evidently involves a continual expenditure of 
energy. It is clear too that deep and rapid breathing or vigor- 
ous heart action must involve an increased activity of the 
muscles concerned. But it is not always clear to what extent 
increased respiratory and heart action are a cause and to what 
extent they are an effect of increased energy metabolism. Thus 
Murlin and Greer ^ emphasize the close relationship of the 
heart to the requirements of the tissues for energy in that the 
energy metabolism is immediately dependent upon oxygen sup- 
ply. Since but little available oxygen can be stored in the hving 
substance, " the response of the heart to variations in the 
(energy) requirement must be immediate and, within very 
narrow limits of time, proportional to this requirement." 
And Benedict states that : 

If subject A, in a resting post-absorptive condition, has on 

a given day a pulse rate of 70 per minute, and on a subsequent 

day under exactly the same conditions has a pulse rate of 60 per 

minute, it may be asserted with every degree of confidence that 

1 American Journal oj Physiology, Vol. a, page 253. 



176 



CHEMISTRY OF FOOD AND NUTRITION 



the metabolism on the second day will be perceptibly, indeed 
measurably, lower than the first. 

A large factor in basal metabolism is the maintenance of 
muscular tension or tone. That every living muscle is always 
in a state of tension is evident from the fact that it gapes 
open if cut. It is equally evident that the degree of tension 
(and therefore the expenditure of energy required to maintain 
it) varies greatly in different individuals under similar conditions 
and in the same individual under different conditions. The 
differences observed by Atwater and Benedict between the 
metabolism of the sleeping hours and that of the hours spent 
sitting up without muscular movement (65 and 100 Calories 
respectively) are largely due to the more complete relaxation 
of the muscles during sleep. Thus there is in the " resting " 
muscle a continual expenditure of energy which first takes the 
form of muscular tension, or tone, but ultimately appears as 
heat, so that the heat production, or energy metabolism, of 
the body at rest depends to a considerable extent upon the 
degree of tension which still persists in the muscles. 

Benedict and Carpenter report the following figures in 
Calories per hour, for the energy metabolism during sleep 
(i A.M. to 7 A.M.) following different conditions of activity 
and showing the after effects of work upon muscular tension 
during rest : 

Energy Metabolism during Sleep — Calories per Hour 



Subject 


Sleep after 
Rest 


Sleep after 

Moderate 

Work 


Sleep after 
Severe 
Work 


Sleep after 

Very Severe 

Work 


E. 

JF.S 

J. C. W 

B. F. D 

A. L. L 


69-3 
60.4 
77.2 
6q.8 
78.3 


74.8 
65.3 


83.1 
83.3 
83.7 


97-9 



CONDITIONS GOVERNING ENERGY METABOLISM 177 

Benedict also finds that even under the most quiet conditions 
a higher tension gradually develops during the waking hours. 
A fasting man metabolized when lying at complete rest 14 per 
cent more in the morning than when sound asleep at night, 
and 22 per cent more in the late afternoon than when asleep. 

Does mental work influence energy metabolism ? — In any 
consideration of this question it is important to distinguish 
sharply between the nervous control of muscular conditions 
and the metabolism of the brain and nerve substance itself. 
As emphasized particularly by Mathews, the brain receives a 
copious blood supply, and the blood coming to the brain is 
arterial, while that leaving the brain is venous, indicating that 
considerable oxidative metabolism occurs in brain tissue. 
Recently also Tashiro has shown that the carbon dioxide pro- 
duction of nerve fiber is increased when the nerve is stimulated 
to activity. But since the entire weight of brain and nerve 
substance constitutes only about 2 per cent of the body weight, 
it remains questionable whether, even if its metaboUsm in- 
creases with " mental activity," the increase would be ap- 
preciable in measurements of the energy expenditure of the 
body as a whole. Probably the best-controlled experiments 
upon this problem, certainly the ones affording most accurate 
measurement of the energy expenditure, are those of Benedict 
and Carpenter, in which a number of college students were given 
course examinations in the respiration calorimeter and their 
energy metabolism during the three-hour period covered by 
the examination was compared with that during the same 
period on another day when the student sat in the calorimeter 
at rest. In some individuals the metabolism was higher during 
the examination period, while in others it was lower — results 
much more likely due to involuntary increase or decrease of 
muscular tension than to altered metabolism of the brain 
tissue. In the average of the entire series of experiments there 
appeared a slight increase of oxygen consumption, carbon 



h 



1 78 CHEMISTRY OF FOOD AND NUTRITION 

dioxide output, and heat production during the examination, 
but the increase was so small and the exceptions so numerous 
that the investigators were not willing to conclude from their 
results that mental work has any positive effect upon the total 
metabolism, but rather infer the opposite. 

Apparently we must conclude that such changes in energy 
metabolism as may result from differences in activity of the 
brain and nerves involved in the performance of mental work 
are so small, in comparison with the energy exchanges always 
going on in the muscles, that the former are quite obscured 
by the unavoidable fluctuations of the latter, and so play no 
measurable part in determining the total food requirement of 
the body. 

Internal secretions, notably that of the thyroid gland, may 
exert a signiiicant influence upon energy metabolism through 
augmenting the heart action and respiration rate, probably 
also through heightened muscular tension, and possibly in 
other ways. Lusk says : " With the possession of such a gland 
as the thyroid, whose suppression may diminish metabolism 
twenty per cent and whose stimulation may increase it loo per 
cent, it is truly strange that the normal person should have a 
basal metabolism so regulated as to correspond to a definite 
heat loss per square meter of body surface." If, however, 
the thyroid gland is conspicuously over- or under-developed 
in size or activity the condition is regarded as a departure 
from health (goiter, myxedema) ; the effect of these and some 
other diseases upon energy metabolism has been summarized 
recently by DuBois^ as follows: 

" Basal metaboHsm is higher than normal in exophthalmic 
goiter, in fever, in lymphatic leukemia and pernicious anemia, 
in severe cardiac disease, and in some cases of severe diabetes 
and cancer. It is lower than normal in cretinism and my.xedema, 
in old age, in some wasting diseases, and perhaps in some cases 

1 Archives of Internal Medicine, Vol. 17, page gi6 (1916). 



CONDITIONS GOVERNING ENERGY METABOLISM 179 

of obesity." " Diseases of the ductless glands other than thy- 
roid show in some cases an increase, in some a decrease; but 
these are comparatively small." 

Benedict ^ also holds, in opposition to some other authorities, 
that "when a carbohydrate-free diet is eaten an acidosis is 
developed which distinctly increases the cellular activity and 
results in a very noticeable increase in the basal metaboHsm." 

In a recent general review of the factors affecting normal 
basal metabolism Benedict ^ concludes "that the basal metab- 
oUsm of an individual is a function, first, of the total mass of 
active protoplasmic tissue, and, second, of the stimulus to cellu- 
lar activity existing at the time the measurement .of the metab- 
olism was made." And that: "Perhaps the most striking 
factors causing variations in the stimulus to cellular activity 
are age, sleep, prolonged fasting, character of the diet, and 
the after effect of severe muscular work." 

Influence of Muscular Work upon Metabolism and Food 
Requirement 

Muscular work is much the most important of the factors 
which raise the food requirements of adults above the basal rate 
necessary for mere maintenance. 

Accurate measurements by means of the calorimeter have 
shown that the average total metabolism of a man sitting still 
is about 100 Calories per hour ; while the same man working 
actively increases his metaboHsm up to about 300 Calories per 
hour ; and a well-trained man working at about his maximum 
capacity metabolizes material enough to liberate 600 Calories 
per hour, i.e. his metabolism may be six times as active during 
the hours actually spent in such work as when he is at rest. 
If during 24 hours a man works as hard as this for 8 hours and 
spends 2 hours in such light exercise as going to and from work, 

* Journal of Biological Chemistry, Vol. 18, page 141 (July, 1914). 

* Proceedings oj the Xulional .-icademy of Sciences, Vol. 1, pages 105-109. 



I So CHEMISTRY OF FOOD AND NUTRITION 

his food requirement for the day will be somewhat over 6000 
Calories, or three times the maintenance requirement. Thus, 
work may increase the day's metabolism as much as 200 per 
cent, whereas liberal feeding at the end of a fast was found to 
increase the metabolism only 22.5 per cent, or one ninth as 
much. Only a few exceptional occupations, such as that of 
lumbermen, for example, involve such heavy work as to cause 
a metabolism of 6000 Calories per day. More often the man 
who works 8 hours a day at manual labor will increase his 
metabolism by 1000 to 2000 Calories above what is needed for 
maintenance at rest, making his total food requirement 3000 to 
4000 Calories. 

Voit estimated the food requirement of a " moderate worker " 
at about 3050 Calories ; and Atwater, in adapting this standard 
to American conditions, increased the allowance to 3400-3500 
Calories in the belief that the American works more rapidly 
and therefore with a greater expenditure of energy. The mis- 
take is often made of supposing that these estimates were in- 
tended for every one who leads an active life, whereas they really 
contemplate a long day of manual labor, for Voit's definition 
of " moderate worker " was a man laboring 9 or 10 hours a day 
at an occupation such as that of a carpenter, mason, or joiner. 

The amount of energy spent during 24 hours by a sedentary 
worker will depend not only upon the number of hours which 
he devotes to exercise, but especially upon the kind of exercise 
chosen. Lusk estimates that an average-sized man sleeping 
8 hours, sitting 14 hours, and walking 2 hours spends about 
2500 Calories ; whereas if he spends 2 hours in vigorous exer- 
cise instead of walking, his total energy output rises to about 
3000 Calories. 

The importance of muscular activity as the chief factor 
governing the energy expenditure and food requirement of 
healthy adults calls for a careful quantitative study of its effect 
upon metabolism. 



CONDITIONS GOVERNING ENERGY METABOLISM 



iSl 



Quantitative relation between work performed and total 
metabolism. — Theoretically it is possible to determine the 
mechanical efficiency of a man by dividing the mechanical 
effect of his work by the increase of energy metaboHsm which 
the work involves. This gives the basis on which to as- 
certain how much extra food would be necessary to supply the 
energy required for the performance of any given task. 

Zuntz and his associates in BerHn have carried out a long 
series of experiments of this kind which are described by Mag- 
nus-Levy in Von Noorden's Metabolism and Practical Medi- 
cine. The general bearing of these experiments may be sum- 
marized as follows : 

The amount of oxygen consumed during work in excess of 
that during rest was regarded as a measure of that expended 
upon the work. As a rule the increased consumption of oxygen 
during work is relatively greater than the increased volume of 
air breathed, so that a greater proportion of the oxygen of the 
inspired air must be taken up by the lungs. As an example 
of the increase of oxygen consumption with muscular work the 
data obtained by Katzenstein in experiments upon the work of 
walking up an inclined plane may be given. The figures were 
as follows : 





Oxygen 
Consumed 
PER Minute 


Respira- 
tory 
Quotient 


Horizontal 
Distance 


Ascent 


At rest 

Walking on very slight incline 

Walking up incline with 10.8 

per cent rise 


cc. 

263.75 
763.00 

1253-2 


0.801 
0.805 

0.801 


Meters 

74.48 
67.42 


Meters 

0.58 
7.27 



The constancy of the respiratory quotient indicates that 
there was no change in the nature of the material burned in the 
body on passing from rest to gentle, or from gentle to moderate 



l82 CHEMISTRY OF FOOD AND XUTRITIOX 

exercise (though there is other evidence, as will be seen below, 
that vigorous exercise is apt to be accompanied by a rise in the 
respiratory quotient). 

The weight moved (that of the subject and his clothing) 
was in this case 55.5 kilograms. From these data it was cal- 
culated that a consumption of energy equivalent to 0.223 kilo- 
gram-meter was required to move i kilogram of weight hori- 
zontally over a distance of i meter; and 2.924 kilogram-meters 
of energy to raise i kilogram through a vertical distance of i 
meter. 

Experiments upon several other subjects gave similar results, 
indicating that these men who, while not trained in an athletic 
sense, were physically sound and thoroughly accustomed to 
this form of exercise, were able to perform i kilogram-meter of 
work in the ascent of the incline with an expenditure of only 
about 3 kilogram-meters of energy over that required at rest, 
so that the work was done with a mechanical efficiency of about 
33 per cent. It is to be noted, however, that this applies only 
to walking done under the most favorable conditions, and not 
carried to the point of fatigue ; also that robust men unac- 
customed to this form of exercise showed efl&ciencies of only 
20 to 25 per cent until after several days' practice, and for some 
subjects the maximum efficiencies found were 21 to 31 per cent. 

On this basis it might be estimated that a man of average 
weight in walking one mile on level ground would do Sooo-9000 
kilogram-meters of work, or about the mechanical equivalent 
of 20 Calories. If this were accomplished with an efficiency of 
33 per cent, it would involve an expenditure of only 60 Calories, 
but at an efficiency of 20 per cent 100 Calories per mile would 
be required. 

The data of Benedict and Murschhauser's recent experiments 
lead to a similar conclusion. They found that the extra metab- 
olism involved in walking at a speed of 4 miles per hour aver- 
aged 0.585 gram-calorie per kilogram-meter. For a man 



CONDITIONS GOVERNING ENERGY METABOLISM 183 

of 70 kilograms this would correspond to an increased energy 
metabolism of about 60 Calories per mile. Very fast walking 
(5.4 miles per hour) involved an expenditure of 0.932 gram- 
calorie per kilogram-meter, equivalent on the same basis to 
about 95 Calories per mile. To walk at a speed of nearly 5^ 
miles per hour required a greater expenditure of energy than to 
run at the same speed. 

These figures may be helpful in estimating the food require- 
ments of men who neither do active physical labor nor take 
vigorous exercise, yet move about more freely than in the so- 
called rest experiments already described. If, for example, 
it be assumed that a healthy man would require 2200 Calories 
per day when remaining in one room, and that the total ad- 
ditional muscular movements of a day at business and recre- 
ation were equivalent to walking five miles on level ground, 
his total food requirement for the day would become 2500 to 
2700 Calories (36 to 39 Calories per kilogram), while activity 
equivalent to walking ten miles on level ground would bring 
the total daily requirements to 2S00 to 3200 Calories (40 to 46 
Calories per kilogram). 

By means of the respiration calorimeter, Atwater and Benedict 
studied the question of mechanical efficiency with more accu- 
rate measurements of the energy involved than in the experi- 
ments of the Zuntz laboratory, but with a different form of 
muscular work. They placed in the calorimeter chamber an 
ergometer, which consisted of a fixed bicycle frame having in 
place of the rear wheel a metal disk which is revolved against a 
measured amount of electrical resistance, so that the mechani- 
cal effect of the muscular work is very accurately determined. 
The expenditure of energy involved in the performance of 
this work was estimated by comparing the total metabolism 
of a working day with that of the same man when living in 
the calorimeter chamber at rest. The average results obtained 
with three different men were as follows: 



1 84 



CHEMISTRY OF FOOD AND NUTRITION 



Subject and Nature of 
Experiment 



Subject E. O. 
Average 13 rest experiments 

(42 days) 

Average 3 work experiments 

(12 days) 

Subject J. F. S. 
Average 4 rest experiments 

(12 days) 

Average 6 work experiments 

(18 days) 

Subject J. C. W. 
Average i rest experiment 

(4 days) 

Average 14 work experiments 

(46 days) 



Energy Transformed 



Total 
per (lay 



Calories 

2279 
3892 

2119 
3559 

2357 
5143 



Excess 

over that 

at rest 



Calories 



1613 



1440 



2786 



Heat 
Equiv. of 
Work Per- 
formed 



Calories 



214 



233 



546 



Mechan- 
ical 
Efficiency 



Per cent 



133 



16.2 



19.6 



With an improved ergometer of the same type as that used in the ex- 
periments just cited, Benedict and Carpenter working with J. C. VV. (one of 
the three men above mentioned) found efficiencies ranging from 20.7 to 22.1 
per cent and averaging 21.6 per cent; with other men studied, the efficien- 
cies ranged from 18. i to 21.2 per cent. 

Benedict and Cathcart, in similar bic\'cle ergometer experiments in which 
the basis of comparison was complete rest on a couch, found efficiencies 
varying from 10 to 25 per cent, depending on load, speed, and the familiarity 
of the subject with the work, the maxima for the six men studied being 
23.1, 20.4, 21.6, 22.7, 20.8, and 25.2 per cent respectively. 

In another series of experiments they subtracted from the expenditure 
of energy during work, the amount spent when the subject, instead of lying 
on a couch, sat on the ergometer and allowed the pedals to be turned under 
his feet. Using this method of estimation they were able by careful adjust- 
ment of speed and load to realize with a professional bicycle rider an efficiency 
of 23 per cent or as much as Zuntz and his associates had estimated from the 
walking experiments. 



CONDITIONS GOVERNING ENERGY METABOLISM 185 

Only under the most favorable circumstances and with 
subjects fully accustomed to the kind of work being performed 
will the actual mechanical effect produced amount to as much 
as one fourth to one third of the extra energy expended during 
work over that during rest, i.e. to an efficiency of 25 to 33 per 
cent. Not only do most occupations involve kinds of work 
which in their nature must be done with less efficiency than 
walking (or riding a stationary ergometer) but the usual hours 
of labor are longer than those in which the maximum mechanical 
efficiency is attained. The efficiency may begin to decline before 
any sensation of fatigue is felt. 

Thus Leo Zuntz found, when he rode his bicycle for four successive hours 
at an average rate of 15 to 17 kilometers (about 9 miles) per hour, that he 
experienced no feeling of fatigue, but his determinations showed that the 
expenditure of energy necessary to produce a given effect had increased 
about 9, 13, 10, and 23 per cent at the end of i, 2, 3, and 4 hours respectively. 
This is because if the same kind of work be performed for a series of hours, 
auxiliary muscles are gradually brought increasingly into action, partly 
for the performance of the work itself, partly for the fixation of the bodily 
framework (maintenance of posture). These auxiliary muscles work less 
economically than those which are used first and most naturally. For 
much the same reasons there is a lower efficiency in the case of work which 
is from the first of too fatiguing a nature because of being either excessive 
or unsuitably distributed. When Leo Zuntz increased his speed 2.4 times, he 
found his metabolism increased 4.3 times, implying a considerable loss of 
efficiency. Under the conditions of Benedict and Cathcart's experiments 
also, the efficiency was usually decreased upon increasing the speed ; on the 
other hand a moderately heavy load was more economical than a light one. 

From the data determined by Atwater and Benedict, Lusk, 
Becker, and their respective collaborators, it is now possible to 
estimate the approximate average expenditure of energy per 
hour under a considerable number of conditions of muscular 
activity. For convenience of comparison and application the 
original data have been reduced to a common basis of a man of 
70 kilograms (154 pounds), then averaged and the average ap- 



l86 CHEMISTRY OF FOOD AND NUTRITION 

proximated to the nearest " round " number, with the results 
shown in the accompanying table. 

Energy Expenditure of Average-sized Man (70 Kilograms) per 
Hour under Different Conditions of Activity. (Approximate 

Averages Only) 

Sleeping 60-70 Calories 

Awake, lying still 70-85 Calories 

Sitting at rest 100 Calories 

Standing at rest 115 Calories 

Tailoring 135 Calories 

Typewriting rapidly 140 Calories 

Bookbinding 170 Calories 

"Light exercise" (bicycle ergometer) 170 Calories 

Shoemaking 180 Calories 

Walking slowly (about 25 miles per hour) 200 Calories 

Carpentry 1 

Metal working > 240 Calories 

Industrial painting] 

"Active exercise" (bicycle ergometer) 290 Calories 

Walking actively (about 3! miles per hour) 300 Calories 

Stoneworking 4°° Calories 

"Severe exercise" (bicycle ergometer) 450 Calories 

Sawing wood 480 Calories 

Running (about 55 miles per hour) 500 Calories 

"Very severe e.xercise" (bicycle ergometer) 600 Calories 

By the use of these estimates the probable food requirement 
for a person of 70 kilograms (154 pounds) may be calculated 
very simply, as, for instance, in the following example : 
8 hours of sleep at 65 Calories = 520 Calories 

2 hours' Hght exercise * at 1 70 Calories = 340 Calories 
8 hours' carpenter work at 240 Calories = 1920 Calories 
6 hours' sitting at rest at 100 Calories = 600 Calories 
Total food requirement for the day, 3380 Calories 
Tigerstedt, in his Textbook of Physiology, gives estimates of 
food requirements for different degrees of activity as indicated 
by means of typical occupations, which may be useful in check- 
ing results calculated as above. 

* Going to and from work, for example. 



CONDITIONS GOVERNING ENERGY METABOLISM 187 

According to Tigerstedt : 

2000-2400 Calories per day suffice for a shoemaker. 
2400-2700 Calories per day suffice for a weaver. 
2700-3200 Calories per day suffice for a carpenter or mason. 
3200-4100 Calories per day suffice for a farm laborer. 
4100-5000 Calories per day suffice for an excavator. 
Over 5000 Calories per day are required by a lumberman. 

Lusk gives the following summary of energy requirements 
of women at work at typical occupations as investigated by 
Becker and Hamalainen in Finland: 

A seamstress sewing with a needle required 1800 Calories. 

Two seamstresses, using a sewing machine, required 1900 
and 2100 Calories, respectively. 

Two bookbinders required 1900 and 2100 Calories. 

Two household servants, employed in such occupations as 
cleaning windows and floors, scouring knives, forks, and 
spoons, scouring copper and iron pots, required 2300 to 2900 
Calories. 

Two washerwomen, the same servants as the last named, 
required 2600 and 3400 Calories in the fulfillment of their daily 
work. 

Benedict and Cathcart find that when muscular work is 
severe there is a rise in the respiratory quotient, the rise being 
greater the more severe the work. In such cases the respiratory 
quotient is found to fall during the rest period following the 
work, and usually to a lower figure than that observed before 
the work was begun. They interpret this to mean that hard 
muscular work draws upon the stored carbohydrate of the body 
in sHghtly greater proportion than upon the stored fat. That 
the work is performed at the expense of both carbohydrate 
and fat is shown by Benedict and Cathcart's data as well as 
by those of many previous experiments. Apparently it is only 
severe muscular activity which has any appreciable influence 



1 88 CHEMISTRY OF FOOD AND NUTRITION 

upon the relative proportions of fat and carbohydrate burned. 
In the experiments cited on page i8i, for example, the respira- 
tory quotient was not changed by walking either on a hori- 
zontal surface or up an inclined plane. It should also be noted 
that Benedict and Cathcart found the same mechanical effi- 
ciency in work whether preceded by a carbohydrate-rich or 
a carbohydrate-poor diet. 

Influence of Food upon Energy Metabolism 

Atwater and Benedict determined directly by means of the 
respiration calorimeter the heat production of the same man 
during five fasting experiments of one to two days each, and 
during a four-day experiment with food about sufficient for 
maintenance. The average total metabolism on the fasting 
days was about 9 per cent lower than on the days when food 
was taken. 

In longer fasts there may be a somewhat greater decrease in 
heat production. Thus, Benedict found that a man who 
weighed at the start 59.5 kilograms (131 pounds) metabolized, 
on the successive days of a seven-day fast, 1765, 1768, 1797, 
1775, 1649, 1553, and 1568 Calories respectively. Naturally 
in long fasts factors other than the simple sparing of the direct 
effect of food come into play.* 

Tigerstedt studied by means of the carbon and nitrogen bal- 
ance the metaboUsm of a man who fasted for five days and 
for the next two days took a very liberal diet. The following 
data were obtained: 

* For a detailed account of the results obtained in a fasting experiment of 31 
days' duration, see Benedict, .1 Study of Prolonged. Fasting, Publication No. 203 
of the Carnegie Institution of Washington. 



CONDITIONS GOVERNING ENERGY METABOLISM 1 89 



ist fast day 

2d fast day 

3d fast day 

4th fast day 

5th fast day 

Fed 4141 Calorics . . . 
Fed 4 14 1 Calories (2d day) 



Body Weight 
Kilos 



67.0 

65-7 
64.9 
64.0 
63.1 
64.0 
65.6 



Calculated 

Total 

Metabolism 

Calories 



2220 
2102 
2024 
1992 
1970 

2437 
2410 



Calories 

PER 

Kilo 



33-2 * 

32.0 * 

31-2 

3I-I 

31-2 

38.1 

36.8 



These results show for man (as had previously been shown 
with dogs) that in fasting the total metabolism continues at a 
fairly constant rate in spite of the fact that the energy is ob- 
tained entirely at the expense of body material. In this case, 
the diet given at the end of the fasting period (4141 Calories) 
was approximately double what would have been required for 
maintenance, but the increase in energy metaboHsm was only 
22.5 per cent over that of fasting. 

The results of fasting experiments thus make it evident that 
the body has but Httle power in the direction of adjusting its 
energy metaboUsm to the energy value of its food supply. 

Rubner found that each type of food exerted a more or less 
specific influence upon the energy metabolism, so that when the 
foodstuffs were fed separately, somewhat different energy values 
were required for the maintenance of body equihbrium. Thus, 
if the total metabolism of a dog fasting at 33° C. be represented 
by 100 Calories, he must be fed, in order to prevent loss of 
body substance, about 106.5 Calories of sugar, or 114.5 Calories 
of fat, or 140 Calories of protein. A man observed by Rubner 
metabolized in fasting 2042 Calories ; when fed 2450 Calories 
in the form of sugar alone, he metabolized 2087 Calories; when 

* These figures are slightly too high because the loss of carbon on these days 
was due in part to combustion of glycogen, but is calculated as if due simply to pro- 
tein and fat. 



IQO CIIKMISTRY OF FOOD AXD XL'TRITKJN 

fed 2450 Calories in the form of meal alone, he metabolized 2566 
Calories. 

Recently Lusk and his coworkers have investigated the in- 
fluence of the foodstuffs upon metabolism (" specific dynamic 
action ") very extensively and have developed the subject to 
such an extent that for an adequate discussion of their results 
the original articles ' or Lusk's own summary - should be con- 
sulted. It appears from this work that when the digestion 
products of carbohydrate or fat are carried by the blood to the 
tissues the energy metabolism (rate of oxidation) rises simply 
because of the increased concentration of oxidizable material ; 
but that some of the products of the digestion and intermediary 
metabolism of protein increase metabolism not only to a greater 
extent, but also in a somewhat different manner, since they seem 
to act as stimuli rather than merely as fuel. On an ordinary 
mixed diet, however, this apparent loss of energy due to eating 
of protein is not a very large factor in the total metabolism, 
since the total specific dynamic action makes the metabolism 
of energy for the day only about one tenth higher on a full 
maintenance ration than when no food is eaten. 

Benedict and Roth have studied the energy metabolism of 
vegetarians as compared with non-vegetarians of the same 
height and weight in order to determine whether or not the 
former maintain a lower plane of basal metabolism than do 
people who eat meat and who are sometimes held to be unduly 
stimulated by the protein of their food. The energy metabolism 
was computed from the carbon dioxide production and oxygen 
consumption determined when the subjects were at complete 
rest and in the " post-absorptive condition," i.e. at least 12 
hours after the last meal, the immediate specific dynamic action 
of the food being thus practically excluded. Under these con- 

• Lusk. Journal of Biological Chemistry, Vol. 20, pages vii-.xvii and 555-617. 
Murlin and Lusk, Ibid., Vol. 22. pages 15-2Q. 

2 Lusk. Science of Nutrition, Third Edition, Chapter X'lL 



CONDITIONS GOVERNING ENERGY METABOLISM 191 

ditions the vegetarian men and women showed average basal 
metaboHsm of 1.06 and 1.025 Calories per kilogram of body 
weight per hour respectively, while the corresponding data for 
non- vegetarian men and women were i.io and 1.04 Calories 
respectively. Benedict holds that these differences are too 
small to establish any essential difference in the basal energy 
metabolism of vegetarians and non-vegetarians of like height 
and weight. 

It is sometimes thought that superior preparation or very 
thorough mastication of food results in such improvement in 
its utihzation that a material saving may be effected in the 
amount of food required. But it will be remembered that 
under average conditions only about 5 per cent of the energy 
value of the food is lost in digestion or expended upon the di- 
gestive process. Any improvement in those conditions through 
superior preparation or mastication of the food can therefore 
at most effect a saving of less than five per cent of the energy 
value. Thus the influence upon total food requirement is 
scarcely appreciable. The advantages of good preparation and 
thorough chewing of the food are very important, but they lie 
in other directions than reduction in the amount of food required. 

Recent scientific evidence supports the view that chronic 
undernutrition or even simple restriction of food consumption 
in health, if continued sufficiently, may bring the organism to 
a lower level of energy metabolism than would be indicated 
by the weight or surface. 

Regulation of Body Temperature 

Climate, season, housing, clothing, are all factors which may 
influence energy metabolism through their bearing upon the 
regulation of body temperature.* It is evident that the main- 

* For full discussion of the influence of surrounding temperature upon metabolism 
and the relation of metabolism to the regulation of body temperature the reader is 
referred to Lusk's Science of Nutrition. 



192 CHEMISTRY OF FOOD AND NUTRITION 

tcnance of the body at a temperature above that of its or- 
dinary environment involves a continual output of heat. This 
output of heat may be regulated in either of two ways: (i) By 
variations in the quantity of blood brought to the skin, which 
tend to control the loss of heat by radiation, conduction, and 
sweating; this is called " physical regulation." (2) By an in- 
crease in the rate of oxidation in the body in response to the 
stimulus of external cold ; such a change in the rate of oxidation 
is known as " chemical regulation." The extra heat production 
which follows the taking of food (the specific dynamic action 
of the foodstuffs) may take the place of the " chemical regu- 
lation " and so help to protect the body from the necessity of 
burning material simply for the maintenance of its temperature. 
Muscular work, by increasing the production of heat in the body, 
may also render chemical regulation unnecessary ; but ap- 
parently the specific dynamic action does not furnish energy 
which can be utilized for muscular work.^ 

The presence of a layer of adipose tissue under the skin as 
well as the custom of covering the greater part of the external 
surface with clothing also tends to keep down the loss of heat to 
the point where " physical regulation " will suffice. Lusk cites 
experiments by Rubner upon a man whose metabolism was 
determined when kept in the same cold room but with dif- 
ferent amounts of clothing, and observes that when the man 
was sufficiently clothed to be comfortable the " chemical regu- 
lation " was eliminated (Science of Nutrition, 3d edition, page 
149). 

In general it seems probable that people warmly clothed and 
living in houses which are heated in winter are not called upon 
to exercise " chemical regulation " to any considerable extent; 
in other words, they probably do not burn any considerable 
amount of material merely for the production of heat, the heat 
required for the maintenance of body temperature being ob- 
1 See Lusk's Science of Nutrition, 3d edition, pages 311-313. 



CONDITIONS GOVERNING ENERGY METABOLISM 193 

tained in connection with the metabolism which is essential to 
the maintenance of the muscular tension and the various other 
forms of internal work. If, however, the body be exposed to 
cold, it may be forced to employ " chemical regulation " with a 
resulting increase of the food requirement, and this will occur 
more readily in a thin person than in one who is well protected 
by subcutaneous fat. 

The extra heat required in cold weather is probably obtained 
for the most part through the activities of the muscles. It is 
a matter of general experience that one instinctively exercises 
the muscles more vigorously in cold weather than in warm, and 
if one attempts to endure much cold without muscular exer- 
cise there results shivering — a peculiar involuntary form of 
muscular activity whose function appears to be to increase 
heat production through increasing the internal work of the 
body. 

To a large extent, therefore, the regulation of body tempera- 
ture, in case of exposure to cold, is accomplished through the 
activity and tension of the muscles. 

The foregoing discussion has reference primarily to adults. 
In the case of the infant whose surface is much greater in pro- 
portion to his weight and whose muscular tone is not yet fully 
developed, the loss of heat to the surroundings is not so readily 
checked by " physical " nor so easily made good by " chemical " 
regulation. Unless the infant is either warmly clothed or sup- 
plied with an artificial source of heat in cold weather he may be 
forced to burn, for warmth, material that might better be em- 
ployed for growth. 

The Influence of Age and Growth 

From the fact that in animals of the same species, but of 

different size the heat production is proportional to the surface 

rather than to the weight, it would follow that children must 

have a greater food requirement per unit of weight than adults. 

o 



194 



CHEMISTRY OF FOOD AND NUTRITION 



In a child 2 years old weighing 25 pounds the energy metabolism 
is approximately half as great as in an adult of six times this 
weight, i.e. the energy expenditure per unit of weight is three 
times as great for the young child as for the resting man, and 
while for the man the expenditure may be taken as a measure of 
the requirement, in the case of the child an additional allowance 
must be made to provide the material retained in the body for 
growth. In studies of infants 7 to 9 months old, Rubner and 
Heubner found a storage of 12.2 per cent of the energy value 
of the food consumed, and Camerer found a storage of 15 per 
cent of the energy and 40 per cent of the protein of the diet. 

The following data from Tigerstedt illustrate the relative 
intensity of metaboUsm at dififerent ages : 





Weight 
Kgm. 


Metabolism per Day 


Subject 


Total 
Calories 


Per Kgm. 
Calories 


Per 

Square Meter 

Calories 


Child, 2 weeks . . . 
Child, 10 weeks . . . 
Child, 10 years . . . 
Man at rest .... 


3-2 

23.2 
70.0 


258 

420 

1462 

2240 


81.0 
84.0 
63.0 
32.0 


1000 
1200 
1499 
1071 



According to these observations the metabolism per unit of 
weight is greatest in infancy and declines steadily with increas- 
ing size ; but calculated per unit of surface it is distinctly less 
in infancy than in children of 10 years, probably because the 
infant sleeps a greater proportion of the time and the tension 
(tonus) of its muscles is not yet fully developed. 

As between children and adults the energy metabolism is 
more nearly proportional to the surface than to the weight ; 
but among children of about the same age the energy require- 
ment may be computed on the basis of weight about as well as 
on th2 basis of surface. 



CONDITIONS GOVERNING ENERGY METABOLISM 195 

Murlin and Bailey estimate from their own observations, 
and the earUer ones of Benedict and Talbot, that the energy 
requirement of the newborn baby kept comfortably warm and 
sleeping quietly may be placed tentatively between 1.7 and 2.0 
Calories per kilogram per hour, the lower figure for a very fat 
(10 lb.) child and the higher for a thin (6 lb.) child. Accord- 
ing to these authors even vigorous crying does not raise this 
figure more than 40 per cent. Benedict and Talbot in their 
later pubhcation ^ give measurements of minimum heat pro- 
duction of 94 newborn infants (2 hours to 6 days old) which 
range from 1.33 to 2.17 Calories, averaging 1.75 Calories per 
kilogram per hour. " Maximum " energy metaboHsm, chiefly 
due to vigorous crying, was also observed in 93 of these cases 
and found to average 65 per cent above the resting value, while 
in several instances (10 out of 93) " crying and extreme rest- 
lessness " resulted in energy expenditure more than double 
that of the same infant at rest. 

With the development of the musculature and of muscular 
tonus, the energy expenditure of the normal infant increases 
for a time even more rapidly than his body weight, so that at 
from 2 nionths to i year of age the expenditure of energy while 
sleeping averages 2.7 Calories per kilogram per hour (average 
of Howland's, Benedict and Talbot's, and Murlin and Hoobler's 
data as summarized by the latter). During the waking hours 
the rate of expenditure is of course materially higher, and in 
calculating food requirements allowance must be made for 
growth and for the possibility of losses through imperfect 
utihzation of the food. In order to provide adequately for all 
contingencies and support the rapid growth which is normal 
at this age, it is estimated that a vigorous child will require 
during the greater part of the first year about 100 Calories of 
food per kilogram of his body weight per day. But in cases 

1 Physiology oj the New Born Infant, Publication No. 233, Carnegie Institution 
of Washington, 1915. 



196 CHEMISTRY OF FOOD AND NUTRITION 

of artificial feeding, since the digestive tract must be gradually 
educated to handle the milk of a different species, it will often 
be necessary to feed much less than 100 Calories per kilogram 
per day at first, perhaps for several months, and only very 
gradually increase the food allowance. 

From the end of the first year until growth is completed the 
food requirement increases, but not so rapidly as does the body 
weight, so that while the allowance of food becomes larger per 
day it becomes smaller per kilogram. On the latter basis the 
energy requirement at the different ages may be estimated 
approximately as follows : 

Under i year 100 Calories per kilogram (45 Calories per lb.) 

1- 2 years 100-90 Calories per kilogram (45-40 Calories per lb.) 

2- 5 years 90-80 Calories per kilogram (40-36 Calories per lb.) 
6- 9 years 80-70 Calories per kilogram (36-32 Calories per lb.) 

10-13 years 75-60 Calories per kilogram (34-27 Calories per lb.) 
14-17 years 65-50 Calories per kilogram (30-22 Calories per lb.) 
18-25 years 55-40 Calories per kilogram (25-18 Calories per lb.) 

Children who are very active or growing very rapidly may 
require even more food than the table just given suggests. 
Such cases are perhaps most frequently found among boys 
between 10 and 15 years of age. DuBois finds in boys 12 and 
13 years old an average basal metabolism (complete rest and 
almost complete fasting) of 1.76 Calories per kilogram per hour, 
or about 75 percent above that of healthy adults.* Assuming 
average activity for boys of this age the energy expenditure 
during 24 hours would probably amount to 60 to 70 Calories 
per kilogram and as this is a period of rapid growth the require- 
ment would be materially higher than the rate of expenditure. 

Assuming average size at the different ages the allowances in 
Calories per day become about as follows : f 

* Per unit of surface the basal energy metabolism of these boys was about 25 
per cent higher than that of healthy men. 

t See also the more detailed table of energy allowances for children in Chapter 
XIV. 



CONDITIONS GOVERNING ENERGY METABOLISM 197 



Children of i- 2 years inclusive 
Children of 2- 5 years inclusive 
Children of 6- 9 years inclusive 
Girls of 10-13 years inclusive 
Boys of 10-13 years inclusive 
Girls of 14-17 years inclusive 
Boys of 14-17 years inclusive 



1000-1200 Calories per day 
1 200- 1 500 Calories per day 
1400-2000 Calories per day 
1800-2400 Calories per day 
2300-3000 Calories per day 
2200-2600 Calories per day 
2800-4000 Calories per day 



In estimating the food requirement of a family it is usually 
preferable to consider each child's energy requirement directly 
rather than to count the children as equivalent to fractions of 
the hypothetical '' average man." 

Above the age of 17 years, although there is still some 
growth, differences in activity due to occupation become so 
great that the food requirement will usually depend as much 
upon occupation as upon age. 

The fuel value of children's dietaries should always be 
liberal in order to provide amply for muscular activity and for 
a more intense general metabolism than that of the adult. 
Furthermore, throughout the period of growth the food must 
supply a certain amount of material to be added to the body 
in the form of new tissue in addition to all that which is oxidized 
to support metabolism. 



Age 


Height 


Weight 


Food Requirement 

WITHOUT Muscular 

Labor 


Years 


Meters 


Feet and 
inches 


Kilos 


Lbs. 


Total per 
day Calories 


Per. Kgm. 

per day 
Calories 


I 

5 
10 

15 
20 
30 
40 
60 
70 
80 


0.70 
1. 00 
1.28 

1. 71 
1.72 
1. 71 


2:3 
4:2 

5:7 + 
5:8- 
5:7 + 


10 

17 
26 

50 
65 
69 
70 
68 
65 
63 


22 

37 

57 

no 

143 
152 
154 
150 
143 
139 


1000 
1400 
1800 
2800 
3000 
2750 
2500 
2300 
2000 
1750 


100 
82 
70 
56 
46 
40 
36 
34 
31 
28 



198 



CHEMISTRY OF FOOD AND NUTRITION 



With the elderly, on the other hand, the intensity of metab- 
oHsm is diminished and the body not only needs less food, 
but has less ability to deal with excess, so that the food re- 
quirement gradually declines and may become 10 or 20 per 
cent, or possibly even 30 per cent, lower than in middle life. 

In the table on page 197 are given the estimated height, 
weight, and food requirement of an average man at different ages, 
the figures for height and weight being based upon the data 
given by Hill for males of the Anglo-Saxon and Teutonic races 
{Recent Advances in Physiology and Biochemistry, page 284). 

These estimates of food requirements are intended to repre- 
sent approximate averages of available data and to allow for 
such exercise as would naturally be taken at the age, exclusive 
of anything which would ordinarily be considered physical 
labor. They thus illustrate in an approximate way the rate 
at which the amount of food required for healthy maintenance 
per unit of body weight declines from infancy to old age. 

DuBois has recently published in graphic form his estimates 
of the basal energy metabolism per unit of body surface at 
different ages. The graph is reproduced by Lusk {Science of 
Nutrition, 3d edition, page 128). 

The average basal metaboHsm, per unit of surface, found by 
DuBois in boys of 12 to 13, in men, and in women was as follows : 

Average Basal Metabolism of Boys, Men, and Women (DuBois) 





Age in Years 


Calorfes per Hour per Square 
Meter 


Subjects 


Computed accord- 
ing to Meeh's 
formula 


Computed by 
Dubois height- 
weight formula 


Boys 

Men 

Women 

Men 

Women 

Men 


12-13 
20-50 
20-50 
50-60 
50-60 
77-83 


45-7 
34-7 
32.3 
30.8 
28.7 


49-9 
39-7 
36.9 
35-2 
32.7 
35-1 



CONDITIONS GOVERNING ENERGY METABOLISM 199 

Influence of sex. — Whether sex shall be said to influence 
the energy requirement will depend upon our use of terms. 
Boys spend on the average more energy than girls, and men 
more than women, but it is doubtful if the differences are due 
to other causes than have been considered above. In experi- 
ments in which children were allowed to move about in a 
small respiration room, boys were found to expend decidedly 
more energy than girls of the same age and weight ; but 
this was probably due to the greater restlessness and muscular 
tension of the boys, for in another series in which both boys 
and girls were kept motionless and relaxed during the obser- 
vations the difference was not found. Benedict and Emmes 
found, as noted above, a slightly higher basal metabolism in 
men than in women of the same height and weight, but 
attribute this to a difference in the average composition of 
the body. 

While sex alone seems not to be a measurable factor in 
energy metabolism, the performance of the reproductive func- 
tions may make large demands upon the maternal organism. 
As weight increases during pregnancy energy metabolism 
increases in at least equal proportion. In the last two weeks 
of human pregnancy Murhn finds the energy metabolism per 
unit of weight about 4 per cent higher than for non-pregnant 
women. During lactation, when the entire nutritive require- 
ment of the nursing infant is being met through the mother, 
the energy needs of the latter are greatly increased. Pro- 
duction of milk involves an extra energy requirement much 
beyond the actual energy value of the milk secreted. While 
accurate determinations are not at hand, it seems safe to 
conclude that the nursing mother taking only moderate 
exercise may need as much food as a man at muscular work. 
Liberal feeding of the nursing mother {e.g. up to 2800 to 
3000 Calories for a woman with moderate muscular exercise) 
is not only important for the conservation of her own bodily 



200 CHEIMTSTRY OF FOOD AND NUTRITION 

resources but may prolong the period of lactation and thus 
be of great value to the child as well.^ 

REFERENCES 

Anderson and Lusk. The Interrelation between Diet and Body Condi- 
tion and the Energy Production during Mechanical Work. Journal of 
Biological Chemistry, Vol. 32, page 421 (1917). 

Armsby. Principles of Animal Nutrition, Chapters 6 and 11. 

Armsby and Fries. Influence of Standing or Lying upon the Metabolism 
of Cattle. American Journal of Physiology, Vol. 31, page 245 (1912). 

Atwater. Neue Versuche ueber Stoff- und Kraft-vvechsel. Ergebnisse 
der Physiologic, Vol. 3 (1904). 

Atwater, Benedict, et al. Respiration Calorimeter E.xperiments. Bul- 
letins 44, 63, 69, 109, 136, 175, Office of Experiment Stations, United 
States Department of Agriculture. 

AuB AND DuBois. The Basal MetaboUsm of Old Men. Archives of 
Internal Medicine, Vol. 19, page 823 (191 7). 

Bailey and Murlin. The Energy Requirement of the Newborn. Amer- 
ican Journal of Obstetrics, Vol. 71, page 526 (1915). 

Becker et al. Energy Metabolism during Different Kinds of Work. 
Skandinavisches Archiv der Physiologic, Vol. 31, (a series of papers) 
— (1914). 

Benedict. Metabolism during Fasting. Carnegie Institution of Wash- 
ington, Publication Nos. 77 and 203. 

Benedict. Factors Affecting Basal Metabolism. Journal of Biological 
Chemistry, Vol. 20, page 263 (191 5). 

Benedict and Carpenter. The Metabolism and Energy Transformations 
of Healthy Man during Rest. Carnegie Institution of Washington, 
Publication No. 126. 

Benedict and Carpenter. The Influence of Muscular and Menf-.l Work 
on Metabolism and the Efficiency of the Human Body as a Machine. 
Bulletin 208, Office of Experiment Stations, United States Department 
of Agriculture. 

Benedict antj Cathcart. Muscular Work : A Metabolism Study with 
Special Reference to the Efficiency of the Human Body as a Machine. 
Carnegie Institution of Washington, Publication No. 1S7. 

Benedict and Emmes. The Influence upon Metabolism of Non-oxidizable 

' For general discussion of the problem of maintaining breast feeding, see papers 
by Sedgwick, Abt, and Hoobler in the Journal of the American Medical Association 
for Aug. II, 1917 (Vol. 69, pages 417-428). 



CONDITIONS GOVERNING ENERGY METABOLISM 20I 

Material in the Intestinal Tract. American Journal of Physiology, 

Vol. 30, page 197 (1912). 
Benedict and Emmes. A Comparison of the Basal Metabolism of Normal 

Men and Women. Journal of Biological Chemistry, Vol. 20, pages 

253-262 (1915). 
Benedict ant) Roth. The Metabolism of Vegetarians as compared with 

Non-Vegetarians of Like Height and Weight. Journal of Biological 

Chemistry, Vol. 20, pages 231-241 (1915). 
Benedict and Smith. The Metabolism of Athletes. Journal of Biological 

Chemistry, Vol. 20, pages 243-251 (1915). 
Benedict and Talbot. Respiratory Exchange of Infants. American 

Journal of Diseases of Children, Vol. 8, pages 1-49 (1914). 
Carpenter. Increase in Metabolism during the Work of Typewriting. 

Journal of Biological Chemistry, Vol. 9, pages 231-266 (191 1). 
Carpenter and Murlin. Energy Metabolism of Mother and Child just 

before and just after Birth. Archives of Internal Medicine, Vol. 7, 

pages 184-222 (1911). 
DuBois. Respiration Calorimetry in Clinical Medicine. Harvey Lec- 
tures, 1915-1916. 
DuBois. The Basal Energy Requirement of Man. Journal of Washington 

Academy of Sciences, Vol. 6, page 347 (1916). 
DuBois. The Metabolism of Boys 12 and 13 Years Old as Compared with 

Metabolism at Other Ages. Archives of Internal Medicine, Vol. 17, 

page 887 (1916). 
DuBois AND Associates. (A Series of Articles on Metabolism in Disease.) 

Archives of Internal Medicine, Vols. 15 and 17 (1915, 191 6). (The 

reader may also find other papers of this series in volumes published 

subsequently to the compiling of this list.) 
DuBois ANT) DuBois. Measurement of the Surface .A.rea of Man. Ar- 
chives of Internal Medicine, Vol. 15, pages 868-881 (1915). 
DuBois AND DuBois. A Formula to Estimate the Approximate Surface 

Area if Height and Weight Be Known. Archives of Internal Medicine, 

Vol. 17, pages 863-871 (1916). 
Gephart ANT) DuBois. Basal Metabolism. Archives of Internal Medicine, 

Vol. 15, page 835; Vol. 17, page 902 (1915, 1916). 
Krogh. The Respiratory Exchange of Animals and Man. 
LowY ANT) ZuNTZ. Influence of War Diet upon the Metabolism. Berlin 

klinische Wochenschrift, Vol. 53, page 825 (191 6). 
LusK. Elements of the Science of Nutrition, 3d edition. 
LusK. The Influence of Food on Metabolism. Journal of Biological 

Chemistry, Vol. 20, pages vii-xvii and 555-617 (1915). 



202 CHEMISTRY OF FOOD AND NUTRITION 

Mathews. Physiological Chemistry, Chapter XIII. 

Means. Basal Metabolism and Body Surface. Journal of Biological 

Chemistry, Vol. 21, pages 263-268 (1915). 
Means, Aub, and DuBois. The Effect of Caffeine on the Heat Production. 

Archives of Internal Medicine, Vol. 19, page 832 (191 7). 
MORGULis. The Influence of Underfeeding and of Subseciuent Abundant 

Feeding on the Basal Metabolism of the Dog. Biochemical Bulletin, 

Vol. 3, page 264 (1914). 
MuRLiN. A Respiration Incubator for the Study of the Energy Metabolism 

of Infants. American Journal of Diseases of Children, Vol. 9, pages 

43-58 (January, 1915). 
MuRLiN AND HooBLER. The Energy Metabolism of Ten Hospital Chil- 
dren between the Ages of Two Months and One Year. American 

Journal of Diseases of Children, Vol. 9, pages 81-119 (February, 1915). 
Murlin and Lusk. The Influence of the Ingestion of Fat. Journal of 

Biological Chemistry, Vol. 22, page 15 (1915). 
SjosTROM. The Influence of the Temperature of the Surrounding .Vir on 

the Carbon Dioxide Output in Man. Skandinainsches Archiv der 

Physiologic, Vol. 30, pages 1-72 (1913). 
SoDERSTROM, Meyer, AND DuBois. A Comparison of the Metabolism of 

Men Flat in Bed and Sitting in a Steamer Chair. Archives of Internal 

Medicine, Vol. 17, page 872 (191 6). 
Talbot. Twenty-four-Hours Metabolism of Two Normal Infants with 

Special Reference to Total Energy Requirement. American Journal 

of Diseases of Children, Vol. 14, page 25 (1917). 
Tashiro. Carbon Dio.xide Production from Nerve Fibers when Resting 

and when Stimulated. American Journal of Physiology, Vol. 32, pages 

107-145 (1913). See also: Proceedings of the National Academy of 

Sciences, Vol. i, page no (1915). 
VoN Noorden. Metabolism and Practical Medicine, Vol. i, pages 20S-282. 
ZuNTZ AND MoRGULis. Influence of Chronic Undernutrition on Metabohsm. 

Biochemische Zeitschrift, Vol. 55, pages 341-354 (1914). 



CHAPTER VIII 

FACTORS DETERMINING THE PROTEIN 
REQUIREMENT 

Animal cells under all conditions of life are constantly break- 
ing down proteins into simpler substances which the body elimi- 
nates. Since this breaking down or " catabolism " of protein 
does not stop either in fasting or under the most liberal feeding 
with fats and carbohydrates, it follows that there is always a 
need for protein whatever the supply of other food. 

Protein metabolism differs widely from energy metabolism in 
the conditions which determine its amount, for protein metab- 
olism is governed mainly by the kind and amount of food, and 
to only a slight extent if at all by muscular exercise ; whereas 
energy metabolism is governed mainly by the muscular exer- 
cise, and to only a relatively small extent by the food. By 
giving food rich in fats and carbohydrates but poor in protein, 
the protein metabolism of a healthy man can easily be brought 
to less than 50 grams per day, and then by changing to a diet 
rich in protein, it may be increased to 150 or even 200 grams 
per day ; i.e. the rate of protein metabolism can be increased 
200 to 300 per cent in a few days by a change in diet alone, all 
other conditions remaining the same. 

Protein Metabolism in Fasting 

Since the diet has such a great influence upon the amount of 
protein metabolized, it might be expected that the basal protein 
metaboHsm could be observed best in fasting. But in fasting 
the energy metabolism of the body is only a little lower than 

203 



204 



CHEMISTRY OF FOOD AND NUTRITION 



with food; the amount of combustion continues nearly the 
same although only body material is available; and since the 
body must consume so much of its own substance to obtain the 
energy needed, there is always a chance that in fasting some pro- 
tein may be burned simply as fuel. Accordingly the protein 
metabolism in fasting may be greater than that which repre- 
sents the needs of the body when properly fed, while on the 
other hand it may be abnormally low through the effort of the 
body to adjust itself to the abnormal condition. 

The amount of protein broken down in fasting is much in- 
fluenced (i) by the previous habit as regards protein consump- 
tion, and (2) by the metabohsm of stored glycogen and stored fat. 

The direct effect of the level of protein metabolism on the days 
preceding the fast is shown in the following data obtained by 
Voit in experiments upon a dog weighing 35 kilograms : 

Influence of Previous Diet on Nitrogen Elimination in Fasting 

(Voit) 







Foods of Preceding Days and Graj£S of Urea 
PER Day 




Meat 2scx> grams 


Meat 1500 grams 


Bread 


Last day with food . 
First day of fasting . 
Second day of fasting 
Third day of fasting 
Fourth day of fasting 
Fifth day of fasting . 
Sixth day of fasting 




180.8 
60.1 
24.9 
19.1 

17.3 
12.3 

13-3 


110.8 
29.7 
18.2 

17-5 
14.9 
14.2 
I3-0 


24.7 
19.6 
15-6 
14.9 
13-2 
12.7 

130 



The influence of the metabolism of the previously stored glycogen 
upon the amount of protein metabolized in fasting is well illus- 
trated by the following three experiments with one individual : ^ 

1 Benedict, Influence of Inanition on Metabolism. Carnegie Institution of Wash- 
ington (1907). 



FACTORS DETERMINING PROTEIN REQUIREMENT 205 





First Day of Fasting 


Second Day of Fasting 


Experiment 


Glycogen metabo- 
lized 


Nitrogen elimi- 
nated 


Glycogen metabo- 
lized 


Nitrogen elimi- 
nated 


I 

II 
III 


grams 
181. 6 

135-3 
64.9 


grams 

5-84 

10.29 

12.24 


grams 
29.7 
18.I 
23.1 


grams 
11.04 
11.97 
12.45 



It will be seen that the nitrogen output was less when 
there was available for metabolism a considerable supply of 
previously stored glycogen. Since most of the stored glycogen 
is used up on the first day of fasting, its influence upon the 
protein metaboHsm is short-lived as compared with that of the 
stored fat. 

The influence of the available supply of body fat upon the 
protein metabolism of fasting is shown by the following obser- 
vations of Falck, on the protein metaboHsm of two fasting dogs 
— the one lean, the other fat : 



Falck 's 


Lean Dog 


Falck 's Fat Dog 


Fasting days 


Grams protein catab- 
olized per day 


Fasting days 


Grams protein catab- 
olized per day 


1-4 


26.1 


1-6 


29.9 


5-8 


24.6 


7-12 


26.7 


9-12 


33-9 


13-18 


26.1 


13-16 


38.0 


19-24 


22.3 


17-20 


31-9 


25-29 


20.0 


21-24 


3-9 


30-34 


16.8 






35-38 


iS-7 


On the 25th day 


the dog died. 


40-44 


130 






45-50 


13.6 






55-60 


12.2 






Dog still healthy after 60 days. 



2o6 CHEMISTRY OF FOOD AND NUTRITION 

A rise in protein metabolism of the lean dog after the 8th day 
showed that from this time he used protein largely as fuel — so 
largely that the results were fatal in 25 days of fasting. The 
fat dog, having plenty of other fuel in the form of fat, used 
protein to a much smaller extent, so that he was able gradually 
to accommodate himself to a lower level of protein metabolism 
and to endure a fast of 60 days' duration. 

The professional faster, Succi, starting with a good store of 
body fat, fasted 30 days* with the following results: 

Five days on ordinary food . . . loi. 4 grams protein per day 

I- 5th days fasting 80.4 grams protein per clay 

6-ioth days fasting 53.1 grams protein per day 

I i-i 5th days fasting 36.2 grams protein per day 

i6-2oth days fasting 33.1 grams protein per day 

2 1-2 5th days fasting 29.3 grams protein per day 

26-3oth days fasting :i3.3 grams protein per day 

Since Succi's health remained good throughout his fast, it 
might be thought that the true protein requirement of his body 
was not greater than the smallest figure found for any period 
— ■ in this case about 30 grams per day. On the other hand, it 
may well be supposed that, since the body increases its protein 
metabolism to an abnormally high rate under influence of exces- 
sive protein feeding, so under the influence of fasting the body 
may be able to adjust itself to an abnormally low rate of pro- 
tein metabolism ; and the fact that the protein metaboHsm con- 
tinues to diminish for such a long time in fasting gives weight to 
the supposition that the body is here gradually adapting itself to 
an abnormal condition. One might assume that in some par- 
ticular period of Succi's fast, the effect of previous feeding might 
no longer be apparent and the conditions had not yet become 
abnormal as the result of the fasting, in which case the ex- 
penditure of protein during one of these periods would represent 
his normal requirement. Any such assumption must, however, 
* The output of nitrogen and of several other elements during a 31-day fast 
recently described by Benedict may be found in Chapter IX. 



FACTORS DETERMINING PROTEIN REQUIREMENT 207 

be more or less arbitrary. A much more definite idea of the 
normal dietary need is obtained by determining experimentally 
how much protein must be contained in the daily food in order 
to keep the body in protein (or nitrogen) equilibrium. 

Nitrogen Balance Experiments and the Tendency toward 
Equilibrium at Different Levels of Protein Intake 

The estimation of the nitrogen balance has already been re- 
ferred to as one factor in the determination of the total food re- 
quirement by means of metabolism experiments ; and it has 
been shown that the balance may be found either by comparing 
the total intake with the total output, or by comparing the 
amount absorbed with the amount cataboHzed and eUminated 
through the kidneys.* When intake exceeds output, there is a 
plus balance which indicates a storage of nitrogen and therefore 
of protein in the body ; a minus balance (greater output than 
intake) indicates a loss of body protein. When the balance is 

0, or so near o as to be within the limits of experimental error, 
the body is said to be in nitrogen {or protein) equilibrium. 

The healthy full-grown body tends to establish nitrogen 
equilibrium by adjusting its rate of protein metaboHsm to its 
food supply within wide limits. The time required by the body 
for this adjustment depends mainly upon the extent to which 
the diet is changed. 

The following observations by Von Noorden illustrate the estab- 
lishment of equiHbrium after only moderate changes in the diet : 

A young woman weighing 58 kilograms (128 pounds) at rest in 
bed was given food furnishing protein, 106 grams ; f at, 7 1 .6 grams ; 
carbohydrate, 200 grams; fuel value, i860 Calories per day. 

* Theoretically the elimination through the skin should also be determined and 
included in the calculation ; practically this is usually neglected unless on account 
of warm weather or vigorous exercise the subject has perspired profusely. For 
data on nitrogen in perspiration see Benedict, Journal of Biological Chemistry, Vol. 

1, page 263 (1906) and A Study of Prolonged Fasting, Publication No. 203 of the Car- 
negie Institution of Washington, pages 233-235. 



2o8 



CHEMISTRY OF FOOD AND NUTRITION 



Example of Adjustment to Diminished Intake 

Total nitrogen of food 16.96 grams 

Lost in digestion (nitrogen in feces) .94 gram 

"Absorbed" 16.02 grams 



Nitrogen Catabolized 

AND ElIKONATED 

THROUGH Kidneys 



Nitrogen Balance 



I St day 
2d day 
3d day 
4th day 
5 th day 




grams 

- 2.18 

- 0.98 
+ 0.22 
+ 0.02 
+ 0.32 



Here there was practical equilibrium after the second day. 
The small amount of nitrogen represented as stored on the 
third, fourth, and fifth days was very likely lost through the 
skin. This was a case of adjustment to a lowered protein in- 
take, for the food previously taken, although not accurately 
observed, was known to have been rich in protein. 

Another experiment was made by Von Noorden with the 
same patient to show the time required to reach equilibrium 
after increasing the intake of protein. In this case the food 
furnished 2030 Calories per day and the nitrogen balance was as 
follows : 

Example of Adjustment to Increased Intake 



Day 


NrrROGEN 
IN Food 


NriROGEN m 
Feces 


Nitrogen 
•' Absorbed " 


Nitrogen 
Catabolized 


Nitrogen 
Balance 




grams 


gram 


grams 


grams 


grams 


I 


14.40 


0.70 


13-70 


13.60 


+ O.IO 


2 


14.40 


0.70 


13-70 


13-80 


— 0.10 


3 


14.40 


0.70 


13-70 


13.60 


+ O.IO 


4 


20.96 


0.82 


20.14 


16.S0 


+ 3-34 


5 


20.96 


0.82 


20.14 


18.20 


+ 1.94 


6 


20.96 


0.82 


20.14 


19-50 


+ 0.64 


7 


20.96 


0.82 


20.14 


20.00 


+ 0.14 



FACTORS DETERMINING PROTEIN REQUIREMENT 209 

Here where the amount of protein fed was increased from 90 
to 130 grams without change in the total fuel value of the diet, 
the body reached equihbrium on the fourth day after the 
increase. 

It is apparent therefore : 

(i) That the body tends to adjust its protein metabolism to 
its protein supply. 

(2) That when the body is accustomed to a certain rate of 
protein metaboHsm, it requires an appreciable length of time to 
adjust itself to a materially higher or lower rate. 

Hence the rate of protein metaboHsm on any given day will 
depend in part upon the rate of metaboHsm to which the body 
has been accustomed and in part upon the protein intake for 
the day. When the protein supply varies from day to day, the 
metabolism for each day is influenced by both the factors, with 
the net result that the elimination equals the intake when 
averaged for a sufficiently long period, although the data for 
any particular day might show a distinct gain or loss. When 
the protein supply is constant for a few days, the effect of pre- 
vious habit usually disappears and equilibrium is established as 
in the above cases. 

A transitory loss of nitrogen from the body is apt to be due 
simply to the taking of less than the usual amount of protein 
food, but a persistent loss indicates that the diet is insufl&cient, 
either in total food (calories) or in protein, to enable the usual 
adjustment to take place. 

A transitory storage of nitrogen in the body may occur as the 
result of an increase either of the protein or of the total fuel 
value of the food ; but a persistent storage occurs, as Von Noor- 
den has pointed out, only under the following conditions : 

(i) In the growing body (or in pregnancy) where new tissue 
is being constructed. 

(2) In cases where increased muscular exercise calls for en- 
largement of the muscles. 



2IO CHEMISTRY OF FOOD AND NUTRITION 

(3) In cases where, owing to previous insufficient feeding or 
to wasting disease, the protein content of the body has been 
more or less diminished and consequently any surplus available 
is utilized to make good the loss. 

Protein-sparing Action of Carbohydrates and Fats 

It has been shown above that, in fasting experiments, the 
amount of stored glycogen and fat in the body exerts a " spar- 
ing " influence upon protein metabolism, the amount of protein 
cataboUzed being smaller when the supplies of glycogen and fat 
are more abundant. Similarly the amounts of carbohydrates 
and fats in the food influence the rate of protein metabolism as 
indicated by the nitrogen excretion. The loss of protein which 
occurs on an insufficient diet may be diminished or even stopped 
by adding carbohydrates or fat to the food ; and if carbo- 
hydrate or fat be added to the diet of a man in nitrogen equi- 
librium, there results a temporary decrease in nitrogen output 
with a corresponding storage of protein in the body. The former 
observation could be interpreted as meaning simply that the 
body draws upon its stored protein for energy so long, and only 
so long, as the fuel value of the food is insufficient ; but the fact 
that addition of carbohydrate or fat to a diet already sufficient 
may cause an actual storage of protein indicates that the " pro- 
tein-sparing action " or " protein-protecting power " of carbohy- 
drates and fats involves something more than merely the question 
whether the body " needs " to burn its stored protein as fuel. 

As this is a matter of great importance, it may be well to 
consider somewhat carefully (i) the experimental evidence, and 
(2) the theoretical explanations, regarding the protein-sparing 
action of the carbohydrates and fats. For an account of the 
earher experiments on this subject, especially those of Voit and 
Rubner upon dogs, the reader is referred to Lusk's Elements of 
the Science of Nutrition. Only some of the more important of 
the experiments upon men can be described here. 



FACTORS DETERMINING PROTEIN REQUIREMENT 21 1 

Lusk/ experimenting upon himself, showed the susceptibility 
of the protein metaboUsm to the sudden withdrawal of carbo- 
hydrate food. In one experiment a liberal mixed diet contain- 
ing 20.55 grams of nitrogen was taken until the body was nearly 
in nitrogen equilibrium, and then, without any other change, 
350 grams of carbohydrate were withdrawn from the daily 
food. On the first day the body protein was largely protected 
by the carbohydrate previously stored in the body in the form 
of glycogen, but on the second day the nitrogen metabolism 
had risen from 19.84 to 27.00 grams per day. In another experi- 
ment, upon a diet containing less protein, withdrawal of carbo- 
hydrate increased the nitrogen excretion from 11.44 to 17.18 
grams per day. 

In these cases, as in the fasting experiments, the loss of body 
protein was less in those subjects having a good store of body 
fat than in those which were thin. 

Kayser compared the efficiency of carbohydrates and fats as 
sparers of protein by observing the effect upon the nitrogen 
balance of replacing the carbohydrates of the food by such an 
amount of fat as would furnish the same number of calories, 
and then' after three days resuming the original diet. This 
experiment and that of Tallquist which follows are given some- 
what fully, as they illustrate well the methods and results of 
investigations based mainly upon the question of nitrogen equi- 
librium. The observer, who served as his own subject, was 
twenty-three years old, of good physique, with a small store of 
body fat, and weighed 67 kilograms. In the first and third 
periods he ate meat, rice, butter, cakes, sugar, oil, vinegar, and 
salad. In the second period the diet was changed so as to con- 
sist of meat, eggs, oil, vinegar, and salad, so that practically all 
the carbohydrate was withdrawn and replaced by fat. The two 
diets had practically the same fuel value and protein content. 
The results of this experiment are shown in the following table : 

' Zeitschrijt fur Biologie, Vol. 27, page 459 (1890). 



212 



CHEMISTRY OF FOOD AND NUTRITION 



Nitrogen Balance when Feeding Isodynamc Quantities of Carbo- 
hydrate AND Fat (Kayser) 







Intake 




Output 
















Nitrogen 


Day 












Total 


Fat 


Carbo- 


Fuel 


Total 


Balance 




nitrogen 


hydrates 


value 


nitrogen 






grams 


grams 


grams 


Calories 


grams 


grams 


I 


21.15 


71. 1 


338.2 


2590 


18.66 


+ 2.46 


2 


21.15 


71.8 


338.2 


2596 


20.04 


+ I.II 


3 


21.15 


71.8 


338.2 


2596 


20.59 


+ 0.56 


4 


21.31 


71.8 


338.2 


2600 


21.31 


=fc 0.00 


5 


21.51 


221. 1 


000.0 


2607 


23.28 


- 1.77 


6 


21.55 


217.0 


000.0 


2570 


24.03 


- 2.48 


7 


21.5s 


215.5 


000.0 


2556 


26.53 


-4.98 


8 


21.10 


70.4 


338.2 


2581 


21.65 


-0.5S 


9 


21.10 


70.4 


338.2 


2581 


19.20 


+ 1.89 


lO 


21.10 


70.4 


338.2 


2581 


19.65 


+ 1.4s 



It is evident from the nitrogen balance of the first period that 
the amount of protein in the food was here greater than neces- 
sary, but that equiUbrium was fully established in four days. 
On substituting fat for carbohydrate there is a marked increase 
of protein catabolism with corresponding loss of nitrogen from 
the body, and what is especially noteworthy, there was no evi- 
dence of any tendency to regain equilibrium during this period, 
but on the contrary the loss of nitrogen became greater each 
day the fat diet was continued ; whereas, upon returning to the 
mixed diet, not only was the loss of protein stopped, but the 
body almost at once began replacing the protein it had lost, 
although the nitrogen and calories of the food were practically 
unchanged. 

Tallquist ^ compared the protein-protecting powers of iso- 
dynamic amounts (amounts having equal energy value) of car- 

1 Archiv Jtir Hygiene, Vol. 41, page 177. 



FACTORS DETERMINING PROTEIN REQUIREMENT 213 



bohydrates and fats when only a part of either was replaced by 
the other. The subject was Tallquist himself, a man twenty- 
eight years old, in good health, and weighing about 80 kilograms. 
The experiment was performed in Rubner's laboratory, and the 
diet contained such an amount of total food as was estimated by 
Rubner to be just about sufficient to supply the energy require- 
ments of the body, viz., 36 Calories per kilogram per day. The 
experiment covered 8 days divided into two equal periods. In 
the first four-day period the diet was rich in carbohydrates, in 
the second period it was rich in fats. An excellent feature of 
this experiment is that there was no change in the nature of the 
protein fed. All foods furnishing any significant amount of 
nitrogen were the same in the two periods of the experiment. 

The food of the first period consisted of meat, milk, butter, 
bread, sugar, coffee, beer. That of the second period contained 
the same amounts of meat, milk, bread, coffee, and beer, but 
less sugar, more butter, and some bacon. The same amount of 
salt was taken in each case. The principal data of the experi- 
ment may be summarized as follows : 

Nitrogen Balance when Feeding Isodynamic Quantities of Carbo- 
hydrate AND Fat (Tallqutst) 









Intake 






Output 


Nitrogen 
Balance 


Day 


Total 
nitrogen 


Fat 


Carbo- 
hydrates 


Alcohol 


Fuel 
value 


Nitrogen 




grams 


grams 


grams 


grams 


Calories 


grams 




I 


16.27 


44.0 


466 


18.5 


2867 


17. II 


- 0.84 


2 


16.27 


44.0 


466 


i8.5 


2867 


14.40 


+ 1.86 


3 


16.27 


44 -O 


466 


18.5 


2867 


14.65 


+ 1.62 


4 


16.27 


44.0 


466 


18.5 


2867 


15.58 


+ 0.69 


S 


16.08 


140.0 


250 


19.0 


2873 


17.66 


-1.58 


6 


16.08 


140.0 


250 


19.0 


2873 


17.32 


- 1.24 


7 


16.08 


140.0 


250 


19.0 


2873 


15.94 


+ 0.14 


8 


16.08 


140.0 


250 


19.0 


2873 


16.22 


— 0.14 



214 



CHEMISTRY OF FOOD AND NUTRITION 



Here only a part of the carbohydrate, about half of that 
present, and an amount representing about one third of the total 
fuel value of the diet, was replaced by fat. The change evi- 
dently had an unfavorable influence upon the nitrogen balance 
but the loss of body protein was relatively small and continued 
only 2 days. 

Atwater ^ compared the protein-sparing action of carbo- 
hydrate and fat in experiments in which the subject, an athletic 
young man of 76 kilos, performed a considerable amount of 
work. The experiments were carried out in the respiration 
calorimeter and covered in all 15 experimental days upon a diet 
rich in carbohydrates, arranged in four periods which were alter- 
nated with four equal periods in which the diet was rich in fats. 
The change from carbohydrate to fat and vice versa involved 
about 2000 Calories or nearly half the fuel value of the diet. 
The average results per day for the entire series of experiments 
were as follows : 





On Diet Rich in 
Carbohydrates 


On D 


ffiT Rich in Fat 


Available Calories in food 






4532 




4524 


Heat equivalent of work 


per- 










formed, Calories . . . 






558 




554 


Nitrogen in food, grams . 






17-5 




17. 1 


Nitrogen in feces, grams . 






2.5 




1-7 


Nitrogen in urine, grams . 






16.6 




18.1 


Nitrogen balance, grams . 






- 1.6 




- 2.7 



Here again there is a difference in favor of the carbohydrate, 
but one which is so small as to be of almost no practical sig- 
nificance. 

It appears that the carbohydrate of the food cannot be en- 
tirely replaced by an equal number of calories in the form of fat 
without an unfavorable effect upon the nitrogen balance; but 

I Ergebuissc dcr Physiologic, Vol. 3, Part I, page 497. 



FACTORS DETERMINING PROTEIN REQUIREMENT 21 5 

that when the replacement is such as to affect not over one half 
of the total calories, the difference in protein-sparing action is 
but slight. Ordinarily on a normal mixed diet the same num- 
ber of calories has about the same protein-sparing effect. 

Landergren ^ also found that it is only when the carbohydrate 
of the diet is entirely replaced by fat that the comparison is so 
strikingly against the fat as it seemed to be in Kayser's experi- 
ment. In Landergren's experiments the condition studied was 
not one of approximate equihbrium, but rather of nitrogen 
hunger. He fed men diets of adequate fuel value but contain- 
ing only about one gram of nitrogen daily, and found that by 
four days of such feeding the urinary nitrogen may be reduced 
to about 4 grams per day. In one experiment in which the daily 
food contained 750 grams of carbohydrates the urine of the 
fourth day showed 3.76 grams of nitrogen. The carbohydrate 
was then entirely replaced by fat, with the result that the fol- 
lowing days' urines contained respectively 4.28, 8.86, and 9.64 
grams of nitrogen. Evidently in the case of a man accustomed 
to feeding largely upon carbohydrates the complete replacement 
of carbohydrate by fat leads to a loss (or an increased loss) of 
body protein. But by subsequent experiments of the same 
series it was found that a diet containing nearly half its calories 
in carbohydrate, and nearly half in fat, had apparently the same 
protein-sparing power as one made up almost exclusively of 
carbohydrates. 

The explanation offered by Landergren is that when the diet 
suppHes no carbohydrate, the glycogen of the body soon be- 
comes exhausted, and the carbohydrate needed, to keep up the 
constant glucose content of the blood is obtained largely by the 
breaking down of proteins. 

This might suffice to explain the difference in effect of carbo- 
hydrate and fat, but not the fact that addition of a non-nitroge- 

• Skandinai'isches Archiv fur Physiologic, Vot 14, page 112 (1903) ; Abstract Ex- 
periment Station Record, Vol. 14, page 1099. 



2l6 



CHEMISTRY OF FOOD AND NUTRITION 



nous nutrient to a diet already sufficient may cause storage of 
nitrogen in the body.* 

A satisfactory explanation of both sets of facts appears to be 
afforded by the recent advances in our knowledge of the fate 
of foodstuffs in metabolism which were outlined in Chapter V. 
The outstanding relationships of the three groups of foodstuffs 
in the intermediary metabolism may be indicated schematically 
as follows : 



CARBOHYDRATE 
Glucose 



FAT 

e.g., Stearin 

^ \ 

Stearic acid Glycerol 

"^ Glyceric 
aldehyde 

^Methyl glyoxal 



By /8-oxidation, 
finally, to carbon 
dioxide and water 



PROTEIN 

.tl. 

Amino acids, 
(Among which) 



Alanine 
4 



Lactic acid H NH3 

^ I 

Pyruvic acid ' 

I 
By oxidation, finally, 
to carbon dioxide 
and water 



Since ammonia is always being formed in protein catabolism 
(by deaminization of amino acids), and since the ammonium salts 
of a-ketonic acids, such as pyruvic acid, are convertible into amino 
acids which are building materials for body protein, we have 
here a mechanism by which an intermediary product of carbo- 
hydrate metabolism (pyruvic acid) takes up a " waste product " 
of protein metaboHsm (ammonia) and turns it back into amino 
acid again. Thus carbohydrate, in undergoing metabohsm, 
" spares " protein, not only by serving as fuel so that protein 

* Furthermore Lusk points out that Landergren's explanation is hardly ade- 
quate to cover the results obtained in gelatin-feeding experiments. 



FACTORS DETERMINING PROTEIN REQUIREMENT 217 

need not be drawn upon for this purpose, but also by furnishing 
material which in combination with ammonia (otherwise a 
waste product) can actually be converted in the body into some 
of the amino acids of which body proteins are composed and 
with which they are in equilibrium. This explains how an in- 
creased intake of carbohydrate, with resulting increase of pyruvic 
acid, naturally leads to increased synthesis of amino acids and 
thus to a tendency toward protein storage, or, to express the 
same thing in somewhat different terms, tends to push the re- 
action, Amino acids ^ Protein, toward the right. 

According to present theory, most, if not all, of the energy of 
the carbohydrate becomes available through oxidation processes 
which involve the intermediate production of pyruvic acid, an 
a-ketonic acid whose ammonium salt is capable of conversion 
into amino acid. Of the fat only the glyceryl radicle (about 
one twentieth of the fuel value) is oxidized through pyruvic 
acid, while the fatty acid radicles, representing about nineteen 
twentieths of the energy of the fat, are metabolized through 
/8-oxidation processes which yield, so far as we know, no product 
whose ammonium salt is convertible into amino acid in the body. 
Hence complete withdrawal of carbohydrate, even though sub- 
stituted by sufficient fat to yield an equal number of calories, 
must be expected to result in increased excretion of nitrogen; 
but when no more than half of the carbohydrate is replaced by 
fat there seems to be enough pyruvic acid produced to meet the 
practical requirements of economical metabolism of protein. 

Protein Requirement in Normal Nutrition 

From what has been said above it will be apparent that, 
within rather wide limits, the greater the amounts of carbo- 
hydrates and fats eaten, the smaller will be the amount of pro- 
tein required to maintain nitrogen equilibrium. 

For practical purposes, however, we may eliminate the ques- 
tion of the extent to which protein metabolism can be restricted 



2l8 CHEMISTRY OF FOOD AND NUTRITION 

by the use of excessive amounts of other food and reduce the 
problem to this : When the total food is properly adjusted to the 
size and activity of the subject so that there is sufficient but 
not excessive fuel to meet all the energy requirements, how 
much protein must the daily food contain in order to keep the 
body in nitrogen equilibrium? 

The most extended investigation on the protein requirement 
of man is that of Chittenden.* The general plan followed in 
this investigation was to have each man reduce his protein food 
gradually without any great change in his other habits. This 
gradual reduction of the protein intake was continued usually 
for some weeks, sometimes for several months, before any com- 
parison of intake and output was attempted. During this pre- 
liminary period upon a restricted diet there was in almost 
every case a loss of weight, and from previous observations f 
under similar conditions we may safely assume that there was a 
considerable loss of body protein. After a suf&cient period of 
adjustment there was usually a tendency for the body weight 
and the rate of protein metabolism (measured by the amount 
of nitrogen eliminated through the kidneys) to become fairly 
constant, indicating that the body had adapted itself to the new 
conditions. When this point had been reached, a nitrogen 
balance experiment was made, the intake and output being 
determined by weighing and analyzing for nitrogen all food 
consumed and all nitrogenous material given off from the body 
except that in the perspiration. The fuel value of the food 
consumed during the same period was calculated by means of 
figures taken from standard tables. From these calculated fuel 
values it would appear that the energy of food consumed by 
Chittenden's subjects was in general about equal to the usual 
estimates of the energy requirements for similar occupations, 

* See Chittenden's Physiological Economy in Nutrition and Nutrition of Man. 

t Neumann, for example, in 35 days on insufficient diet lost 96 grams of nitrogen 
corresponding to 600 grams of protein, equivalent to about 2.5 kilograms (5.5 pounds) 
of muscle tissue. 



FACTORS DETERMINING PROTEIN REQUIREMENT 219 

though in several specific instances the subject may have unduly 
restricted his total food intake and thus created an energy 
deficit and a tendency toward negative nitrogen balance. 

Chittenden bases his estimate of the protein requirement, not 
only upon the nitrogen balances, but also upon the amounts 
of nitrogen observed to be eliminated daily through the kidneys 
over long periods in which the body may or may not have been 
in cornplete equihbrium, but in which health and efficiency were 
certainly maintained. The first men to serve as subjects in this 
investigation were Chittenden himself and his associates, who 
all continued their professional work and either reported no 
effect or felt benefited by the change to the low protein diet. 
Similar experiments were then made upon a squad of soldiers, 
who during the test were quartered near the laboratory and were 
given regular exercise in the gymnasium in addition to light 
duties about their quarters. These men showed marked im- 
provement in physical condition during the test, probably due 
in part to their more regular habits of life and their gymnastic 
exercises. In order to eliminate this latter factor while still 
applying the low protein diet to young and physically active 
men, the investigation was extended to cover a group of uni- 
versity athletes who were already well-trained and in prime 
physical condition at the beginning of their dietary experiment. 
These athletes not only maintained, but in many cases improved, 
their gymnastic records while on the low protein diet, one of 
them winning an all-round gymnastic championship during 
the time. Chittenden states ^ that his data " are seemingly 
harmonious in indicating that the physiological needs of the 
body are fully met by a metaboHsm of protein matter equal to 
an exchange of o.io to 0.12 gram of nitrogen per kilogram of 
body weight per day, provided a sufficient amount of non- 
nitrogenous foods is taken to meet the energy requirements of 
the body." This would correspond to 44 to 53 grams of pro- 

1 Nutrition of Man, pages 226, 272. 



220 CHEMISTRY OF FOOD AND NUTRITION 

tein per day for a man of average weight (70 kilograms, 154 
pounds, without clothing), and Chittenden considers that for 
such a man an allowance of 60 grams of protein per day should 
certainly be entirely adequate. 

In a recent examination of the available Hterature upon this 
subject there were found 86 experiments upon adults showing 
no abnormality of digestion or health, in which the diet was 
sufficiently well adjusted to the probable requirement and the 
nitrogen balance showed sufficient approach to equilibrium to 
make it appear that the total output of nitrogen might be taken 
as an indication of the protein requirement. These experi- 
ments are taken from 20 independent investigations in which 41 
different individuals (37 men and 4 women) served as subjects. 
For purposes of comparison the daily output of total nitrogen in 
each experiment was calculated to protein and this to a basis of 
70 kilograms of body weight. Reckoned in this way, the ap- 
parent protein requirement as indicated by the data of individual 
experiments ranged between the extremes of 20.0 and 79.2 grams, 
averaging 49.2 grams of protein per man of 70 kilograms per day. 
Thus the average falls well within the range of Chittenden's 
estimate of the amount of protein required for normal nutrition 
when the energy value of the diet is adequate. 

Examination of the data recorded in the original papers indi- 
cates that the wide differences in amounts of protein catabolized 
in the different experiments cannot be attributed primarily to 
the kind of protein consumed nor to the use of diets of fuel 
values widely different from the energy requirements. Ap- 
parently the most influential factor was the extent to which the 
subject had become accustomed to a low protein diet. 

Difference between Minimum Requirement and Standard 
Allowance of Protein 

It may be well to point out here the distinction between the 
amount of protein actually required on the one hand, and, on 



FACTORS DETER^IINING PROTEIN REQUIREMENT 2 21 

the other hand, the amount which it may be thought best to 
allow in the planning of dietaries. The term " requirement " 
should preferably be applied only to the former; the latter 
would better be called the protein allowance or the standard 
for protein. The difiference between the amount actually re- 
quired and the amount which would ordinarily be allowed in 
planning a dietary is much greater with protein than with fuel 
value. Surplus fuel is stored as fat, and if excessive fatness is 
to be avoided, the fuel value of the food must not greatly exceed 
the energy requirements of the body; but surplus nitrogen is 
rapidly eliminated from the body and, so long as no injury to 
health results, leaves no evidence of having been taken in excess 
of body needs. The eating of a considerable surplus of protein 
has become habitual, and such a surplus of protein in the food 
is beheved by many people to constitute a desirable " factor of 
safety," if not indeed to exert a directly beneficial effect upon 
health and stamina. Hence there is a tendency to set the pro- 
tein allowance or standard for protein considerably higher than 
the actual requirement. 

If the average daily food requirement of a man at rest be 
taken as 2000 Calories including 50 grams of protein, the same 
man at work may require 3000 or 4000 Calories while his actual 
requirement for protein will not be appreciably increased. If 
the protein be held at 50 grams while the food is increased from 
2000 to 3000 to 4000 Calories, the protein in percentage of total 
calories would be in the three cases 10 per cent, 7 per cent, and 
5 per cent respectively. Thus it is plain that when the energy 
requirement is subjected to considerable variations by differ- 
ences in muscular activity, the protein requirement cannot be 
taken as constituting a fixed proportion of the total calories, 
since muscular work increases the energy requirement very 
greatly and the protein requirement very little if at all. In 
practice, however, a diet of 2000 Calories would usually contain 
somewhat over 50 grams of protein ; and when the man increased 



222 CHEMISTRY OF FOOD AND NUTRITION 

his activity and his total food consumption, he would probably 
increase his protein intake in almost the same proportion, for 
he would in most cases simply eat a larger quantity of his usual 
kind of food. 

Moreover, those differences in food requirement which are 
due to differences in age and size will usually afTect the energy 
requirement and the protein requirement in about the same 
proportion ; and, as the majority of dietaries are planned for 
family groups, the differences in age and size are usually quite 
as important as the differences in muscular activity. Thus 
there is rational basis for the custom of allowing enough pro- 
tein to furnish from lo to 15 per cent of the total energy value 
of the diet. 

Influence of the Choice of Food 

When isolated proteins are fed singly, striking differences in 
nutritive value appear, as has been shown in Chapter III. In 
view of this fact it may seem strange that in the experiments 
hitherto conducted to determine the protein requirement of 
man the kind of protein fed has not exerted a more striking 
influence upon the results obtained. There is, however, no 
real discrepancy between the two sets of findings. The experi- 
ments described in Chapter III were for the purpose of compar- 
ing individual proteins isolated even from the other proteins 
which always accompany them in natural or commercial food 
materials, and were conducted largely upon rapidly growing 
young animals, in which there is an active synthesis and reten- 
tion of protein, so that a deficiency in the supply of any amino 
acid which is required in the construction of body protein is apt 
to be quickly and plainly reflected in a diminution or cessation 
of growth. On the other hand, in experiments like those de- 
scribed in the preceding section, where the purpose is not to 
compare proteins but to measure the normal protein require- 
ment, the diet is naturally made up, not of isolated proteins or 



FACTORS DETERMINING PROTEIN REQUIREMENT 223 

even of single or unusual foods, but (ordinarily at least) of such 
combinations of staple foods as is believed to represent a normal 
diet, so that even a relatively simple ration arranged for the 
purposes of such an experiment would probably contain a num- 
ber of different proteins among which any peculiarities of amino 
acid make-up would be apt to offset each other. Moreover the 
experiments of the latter group have been made entirely upon 
adults whose protein requirement was limited to that of main- 
tenance. In such cases there is no longer a demand for amino 
acids to be built into new tissue, but only to maintain the equi- 
librium which now exists between amino acids and proteins in 
the tissues already full grown. Any of the amino acids whose 
radicles are contained in tissue proteins may be expected to 
contribute something to the maintenance of such an equilibrium, 
whereas there can be no growth unless all the necessary amino 
acids are present. In a corresponding series of experiments 
upon growing children or nursing mothers the influence of food 
selection would probably be much more pronounced. 

Even for the maintenance of adults protein requirement may be found 
to be considerably influenced by food selection when experiments suitably 
planned to test the question are carried out. The inadequacy of gelatin as 
a sole protein food and its inferiority to meat or milk protein when substi- 
tuted beyond a certain proportion are well known. A series of experiments, 
designed to demonstrate differences in nutritive efficiency for man of the 
protein supplied by different staple articles of food, was carried out by Karl 
Thomas in Rubner's laboratory and the striding results obtained have been 
widely quoted, often on Rubner's authority. These results, however, have 
as yet failed of confirmation, and on some important points have been so 
directly refuted by later workers using longer experimental periods, as to 
make it appear that Thomas's plan of experimenting and mode of inter- 
pretation were not entirely suited to the solution of the question at issue. 

Thomas! thought he had demonstrated that meat protein was greatly 
superior to bread or potato protein for the maintenance of body tissue ; 
but Hindhede finds no such difference, being able to maintain normal nutri- 
tion \\ith either bread or potato nitrogen in relativ'ely small amounts. 

* Thomas, Archiv JUr Anatomic und Physiologic, igog, pages 210-302. 



224 CHEMISTRY OF FOOD AND NUTRITION 

Rose and Cooper * have also demonstrated the high value of potato 
nitrogen in the maintenance of nitrogen equilibrium, and preliminary ex- 
periments in the writer's laboratory f have tended to confirm Hindhede's 
finding that nitrogen equilibrium may be maintained on a relatively low 
intake of protein in the form of bread. 

Of greater practical importance than the experiments with bread alone 
are those f which show the maintenance of nitrogen equilibrium over long 
periods on low protein diets in which bread is the chief source of protein, 
but is supplemented by small amounts of milk. 

Since estimates of protein requirement, in order to be of 
general application, should provide for the needs of growth, 
reproduction, and lactation, as well as for maintenance, it will 
be well to consider more fully the results obtained in feeding 
experimental animals upon known rations throughout the period 
of growth or the entire life cycle. 

It will be remembered that Osborne and Mendel, feeding 
isolated proteins in liberal proportion (i8 per cent) in diets 
adequate and well balanced as regards all other factors, found 
that edestin, a typical vegetable globulin, was able to supply all 
the protein requirements of maintenance, reproduction, and 
growth, even through three generations of rats. With gliadin 
as the sole protein, maintenance was satisfactory but growth 
was inhibited ; but an addition of lysine to this diet caused an 
immediate resumption of growth. When the supply of lysine 
was cut off, growth again ceased. A ration containing zein as 
the sole protein did not suffice even for maintenance ; but when 
tryptophane was added to it, or gliadin, which contains trypto- 
phane, it served to maintain body weight, and on further addition 
of lysine, growth ensued. 

In order to emphasize such differences as these it is some- 
times thought advantageous to classify proteins as : 

A. Complete : Capable of maintaining adults and providing 
for normal growth of the young when used as a sole protein 

* Rose and Cooper, Journal of Biological Chemistry, Vol. 30, pages 201-204. 
t Not yet published. 



FACTORS DETERMINING PROTEIN REQUIREMENT 225 

food. Casein and lactalbumin of milk; ovalbumin and ovo- 
\dtellin of egg ; glycinin of soy bean ; excelsin of Brazil nut ; 
edestin, glutenin, and maize-glutelin of the cereal grains. 

B. Partially Incomplete: Capable of maintaining life but 
not of supporting normal growth. Gliadin of wheat is the well- 
demonstrated example of this class. 

C. Incomplete : Incapable either of maintaining Hfe or of 
supporting growth, when fed as the sole protein. Zein of corn 
(maize), and gelatin are the conspicuous examples. 

Any such grouping of the proteins, however, must be used 
with much discrimination, and with great care to insure an 
understanding of the quantitative aspects of the experimental 
data, if misconceptions are to be avoided. Edestin is a con- 
spicuous example of a " complete " protein, having served as 
above noted as the sole protein food of a family of rats for three 
generations; but when the percentage of edestin in the food 
mixture was considerably reduced, results like those above 
described for gliadin were obtained — the diet did not support 
a normal rate of growth, but this could be secured by adding 
lysine to the food mixture. Similarly casein when fed in reduced 
proportion to the total food mixture did not support normal 
growth ; but growth became normal when cystine was added. 
Thus " complete " proteins may behave as " partially incom- 
plete " when fed in reduced proportion. It is also to be remem- 
bered that varying rates of growth in different species (not 
to mention other differences) make inadmissible any broad 
generaUzations as to the proportion in which any protein should 
be fed to species other than that with which its " completeness " 
or " incompleteness " has been demonstrated. 
. In some of their most recently published experiments (1916) 
Osborne and Mendel give quantitative measurements of the 
relative efficiency (for support of growth in young rats) of some 
of the " complete " proteins. The rate of gain obtained with 
8 per cent of lactalbumin required 12 per cent of casein or 15 
Q 



2 26 CHEMISTRY OF FOOD AND NUTRITION 

per cent of edestin ; or, as they also state the result, " to pro- 
duce the same gain in body weight 50 per cent more casein 
than lactalbumin was required, and of edestin nearly go per 
cent more." In maintenance experiments, 2.4 to 3 per cent of 
lactalbumin was as effective as 3.5 to 4 per cent of casein or 
edestin. 

On extending their experiments from rats to chicks, Osborne 
and Mendel again found that proteins rich in lysine are much 
more effective for growth than those in which the proportion of 
lysine is much smaller. 

McCollum found milk protein much more efficient than 
wheat or maize protein in supporting the growth of young 
pigs. 

As in growth, so in lactation, the demand for material for the 
construction of new protein creates a condition in which differ- 
ences of value in the protein fed may readily become more ap- 
parent than when only maintenance is involved. Hart and 
Humphrey find that in meeting the protein requirements of 
milch cows, milk protein and the protein of flaxseed, " oil meal," 
are about 50 per cent more efficient than the proteins of the corn 
(maize) or of the wheat kernel; and Hoobler has shown that 
milk is the best form of food protein for the production of 
human milk and the protection of the body protein of the nurs- 
ing mother. 

Influence of Muscular Exercise 

At one time it was supposed that muscular power was gener- 
ated at the expense of muscle substance and this, of course, 
necessitated the belief that muscular work always increased pro- 
tein metabolism. Since we now know that the muscles work 
quite as well at the expense of carbohydrates and fats as of pro- 
tein, the conclusion that muscular work necessarily increases 
the metabolism of protein is far from inevitable. It is only 
necessary to observe the effects of regular muscular exercise, 



FACTORS DETERMINING PROTEIN REQUIREMENT 227 

either in athletic training or in normal labor, to see that the 
muscles do not waste away when thus used, but rather tend to 
become larger. Such a growth of the muscles tends toward a 
storage rather than a loss of protein. Usually, however, mus- 
cular work also results in increased appetite, and it is difficult 
to separate the effects of the exercise from those of the extra 
food. 

Whether muscular work acts directly to increase the amount 
of protein metabolized in the body can only be determined by 
experiments in which sufficient extra fats and carbohydrates 
are fed to furnish the extra fuel required on the working days. 
But since fats and carbohydrates spare protein, the feeding of 
these in any excess over just what is necessary to provide for the 
increased energy requirement would tend to decrease the metab- 
olism of protein and counteract any effect which the muscular 
work might otherwise have in increasing protein metabolism. 
Hence, in order to show conclusively whether muscular work of 
itself has any influence upon the protein metabolism, it would 
be necessary to determine the mechanical efficiency of the man, 
then to bring him into equihbrium with an amount of food just 
sufficient for his needs, and finally to have him perform a meas- 
ured amount of work at the same time adding to his diet an 
amount of fats and carbohydrates just sufficient to furnish the 
extra energy required for the work performed. Such elaborate 
experiments have not yet been made, but we have sufficient 
data to show that they are not necessary for practical purposes. 
Many experiments have shown conclusively that increased work, 
when accompanied by a sufficient increase in the amount of fats 
and carbohydrates fed, does not necessarily increase the metab- 
olism of protein. 

The following data from Atwater {Report of the Storrs, Con- 
necticut, Agricultural Experiment Station for igo2-igoj, page 
127) show the average results of a long series of rest and work 
experiments with men in the respiration calorimeter : 



228 CHEMISTRY OF FOOD AND NUTRITION 

Muscular Work and Protein Metabolism (Atwater) 



Nature of Experiment 



Resl: Food generally sufficient 
for equilibrium ; 5 subjects, 
27 experiments, covering 82 
clays 



Work : 8 hours per day. Food 
generally not quite sufficient 
for equilibrium; 3 subjects, 
24 experiments, covering 76 
days 



Average Metabolism per Day 



Per Person 



Energy, 
Calories 



2310 



4556 



Protein, 
Grams 



103.8 



Per Kilogram 
Body Weight 



Energy, 
Calories 



33-5 



62.9 



Protein, 
Grams 



I-5I 



1.49 



Per Square 
Meter Surface 



Energy 
Calories 



1116 



2129 



Protein, 
Grams 



SO. I 



50.5 



Comparing the figures either per unit of weight or of surface, 
it will be seen that muscular work sufficient to nearly double 
the energy metabolism had no appreciable effect upon the 
amount of protein metabolized. Considering the large amount 
of exceptionally accurate research represented in these 
figures, they seem to justify the conclusion that if muscular 
work has any tendency to increase the " wear and tear " of 
muscle substance, such effect is normally balanced by the tend- 
ency of the muscles to grow (and therefore store protein) when 
exercised. 

Moreover, it is certain that any effect which muscular work 
might possibly have in increasing protein metabolism would be 
incomparably less than its effect in increasing the total metab- 
oHsm. If, then, starting with a diet which maintains protein 
equiHbrium at rest, the total food is increased sufficiently to 
provide for the muscular work, and the increase in the diet is 



FACTORS DETERMINING PROTEIN REQUIREMENT 229 

accomplished by adding any reasonable combination of food 
materials, we may feel sure that these will supply plenty of 
protein to meet any possible increase in the protein requirement. 
Hence, in planning the diet of a man at hard muscular work, 
any reasonable combination of foodstuffs given in sufficient 
abundance to meet the energy requirement will almost certainly 
supply an ample amount of protein. 

Shafi[er has studied the output of ammonia, creatinine, and 
uric acid as well as of total nitrogen during rest and work and 
finds no significant change in any of these. Lusk considers it 
fully proved that neither the amount nor the character of pro- 
tein metabolism is changed by muscular activity. 

Protein Requirement in Relation to Age and Growth 

If a man at moderately active work takes a diet which fur- 
nishes 3000 Calories and 75 grams of protein, he is taking 10 
per cent of his calories in the form of protein. Of course the 
protein requirement cannot bear a fixed relation to the calorie 
requirement, since the latter is largely influenced by activity, 
while the former is not. Most men, when at complete rest, 
would require more than 10 per cent of their calories in the form 
of protein because the lack of exercise would not reduce the 
protein requirement to the same extent as the energy require- 
ment. On the other hand, most Americans are accustomed to 
take more than 10 per cent of their calories as protein regardless 
of whether they require it or not. If, then, the active man's 
need for protein is met by supplying him with 10 per cent of 
his needed calories in the form of protein, this will serve as a 
convenient starting point in considering the requirements of a 
child. Let this be compared with the normal dietary of an 
infant. Human milk averages about 1.6 per cent protein, 4.0 
per cent fat, 7.0 per cent carbohydrate. Here about 9 per cent 
of the calories are taken in the form of protein, or about the 
same proportion as has been allowed for the full-grown active 



230 CHEMISTRY OF FOOD AND XUTRmON 

man. Furthermore Hoobler has shown experimentally that 
this is as high a proportion of protein as the infant will utilize 
with the highest efficiency in growth of body tissue. During 
the suckling period the growth is relatively more rapid than at 
any other age. Mendel * gives the following figures : 

The Relative Daily Gain in Body Weight of Children 

In the first month is about i.oo per cent 

At the middle of the first year 0.30 per cent 

At the end of the first year 0.15 per cent 

At the fifth year 0.03 per cent 

Maximum in later years 

for boys 0.07 per cent 

for girls 0.04 per cent 

If, then, the full-grown man and the child at the time of most 
rapid growth each requires but 10 per cent of his calories in the 
form of protein, it seems probable that this proportion is also 
sufficient for any intermediate age, if the diet is of ample fuel 
value, and the protein is of the right kind. But the proper 
selection of the protein is of very great importance in the feeding 
of children, who differ from most other young mammals in that 
their period of growth is so many times longer than the suckling 
period. Even the child that is nursed for a year and attains 
three times his birth-weight before weaning will still have much 
the greater part (probably five sixths) of his growth to make 
on other food. By the time growth is complete he will prob- 
ably have about twenty times the body weight and more than 
twenty times the body protein with which he was born. 

Growth at the normal rapid rate of early childhood involves 
the conversion of a very considerable part, sometimes as much 
as one third, of the protein of the food into body protein. This 
can be accompHshed to the best advantage only when (i) the 
protein of the food is largely of the kind most efficient in sup- 
porting growth, /c. milk protein; (2) the protein is well " pro- 

* Childhood and Growth, p. 18. 



FACTORS DETERMINING PROTEIN REQUIREMENT 231 

tected " by the protein-sparing action of liberal amounts of 
carbohydrate and fat. 

That the child needs a diet of high fuel value to meet the 
requirements of his energy metabolism has already been pointed 
out (Chapter VII). It is because the high protein requirement 
of childhood (for young children more than twice as much per 
unit of weight as for adults) is paralleled by an equally high 
energy requirement that the diet of the child need not contain 
a higher percentage of its calories in the form of protein than 
does the ordinary diet of the adult, if the protein for the child 
is well chosen. 

Usually, however, a well-planned dietary for a child will show 
a somewhat more than average proportion of its calories in the 
form of protein because after weaning the main feature of the 
child's diet should be cows' milk which furnishes about 19 per 
cent of its calories in the form of protein. A child, fed mainly 
upon cows' milk and taking enough food to amply cover his 
energy requirement, will therefore receive a safe surplus of pro- 
tein in the best available form. With a full quart of milk in 
the daily dietary of the growing child the other foods may be 
selected chiefly with reference to other quahties than their pro- 
tein content; without a liberal use of milk the proper feeding 
of a growing child becomes a very difficult problem. 

Having discussed the protein requirements of ordinary adult 
maintenance and of growth, the requirements of the aged should 
also be considered. This does not require extended discussion, 
since advancing age involves no new features but only a gradual 
modification of those pertaining to middle life. 

In general, elderly people show a somewhat diminished pro- 
tein requirement and likewise a diminished power of dealing 
with excess. Surplus protein taken in the food is not so rapidly 
absorbed and catabolized, and, while there appears to be no 
essential difference in the form in which the nitrogen is finally 
excreted, the susceptibility to excessive putrefaction of protein 



232 CHEMISTRY OF FOOD AND NUTRITION 

appears to be increased. It would seem that in the dietary of 
the aged the protein should be reduced to at least as great an 
extent as are the calories. 

REFERENCES 

Atwater and Benedict. Comparison of Fats and Carbohydrates as 
Protectors of Body Material. Bulletin 136 (pages 176-187), Office 
of Experiment Stations, U. S. Dept. Agriculture. 

Benedict. The Influence of Inanition on Metabolism (Publication 77) 
and A Study of Prolonged Fasting (Publication 203). Carnegie Insti- 
tution of Washington. 

Catiicart. Physiology of Protein Metabolism. 

Chittenden. Physiological Economy in Nutrition. 

Chittenden. The Nutrition of Man. 

Hart and Humphrey. The Relation of the Quality of Proteins to Milk 
Production. Journal of Biological Chemistry, Vol. 21, page 239 (1915) ; 
Vol. 26, page 457 (1916) ; Vol. 31, page 445 (iQi?)- 

Hint)hede. Protein and Nutrition. 

Hindhede. Nutritive Value of the Proteins of Potatoes and of Bread. 
Skandinavisches Archivf. Physiologic, Vol. 30, page 97 (1913) ; Vol. 31, 
page 259 (1914). 

Hoobler. The Protein Need of Infants. American Journal of Diseases 
of Children, Vol. 10, page 153 (1915). 

Hoobler. The Effect on Human Milk Production of Diets Containing 
Various Forms and Quantities of Protein. American Journal of Dis- 
eases of Children, Vol. 14, page 105. See also Journal American Medical 
Association, Vol. 69, page 421 (August, 1917). 

LusK. Elements of the Science of Nutrition. 

McCoLLUM. The Nature of the Repair Processes in Protein Metabolism. 
American Journal of Physiology, Vol. 29, page 215 (1912). 

McCoLLUM. The Value of the Proteins of Cereal Grains and of Milk, for 
Growth in the Pig. Journal of Biological Chemistry, Vol. 19, page 323 
(1914). 

McCoLLUM and Davis. Influence of the Plane of Protein Intake on Growth, 
Journal of Biological Chemistry, Vol. 20, page 415 (1915). 

McCoLLUM, SiMMONDS, ANT) PiTz. Effects of Feeding the Proteins of the 
Wheat Kernel at Different Planes of Intake. Journal of Biological 
Chemistry, Vol. 28, page 211 (1916). 

McKay. The Protein Element in Nutrition. 



FACTORS DETERMINING PROTEIN REQUIREMENT 233 

Mendel. Nutrition and Growth. Harvey Society Lectures, I9i4-i9i5,and 
Journal of the American Medical Association, Vol. 64, page 1539 (1914). 

MuRLiN. The Nutritive Value of Gelatin. American Journal of Physi- 
ology, Vol. 19, page 285; Vol. 20, page 234 (1907-1908). 

MuRLiN AND Bailey. Protein Metabolism in Normal Pregnancy. Ar- 
chives of Internal Medicine, Vol. 12, page 288 (1913). 

Osborne and Mendel. (A Series of papers upon the nutritive functions 
and relative efficiency of individual proteins and amino acids in main- 
tenance and growth.) Journal of Biological Chemistry, Vol. 1 2, page 473 ; 
Vol. 13, page 233 (1912); Vol. 17, page 325; Vol. 18, page i (1914) ; 
Vol. 20, page 351 ; Vol. 22, page 241 (1915) ; Vol. 25, page i ; Vol. 26, 
pages I, 293 (1916). (Subsequent issues should also be consulted for 
papers appearing after the compilation of this list.) 

Rose and Cooper. The Biological Efficiency of Potato Nitrogen. Jour- 
nal of Biological Chemistry, Vol. 30, page 201 (191 7). 

SrvEN. (Experiments on Protein Requirement.) Skandinavisches Archiv f. 
Physiologic, Vol. 10, page 91; Vol. 11, page 308. 

VoN NooRDEN. Metabolism and Practical Medicine, Vol. i, pages 283-383. 

Wilson. Nitrogen IMetabolism during Pregnancy. Bjilletin of the Johns 
Hopkins Hospital, Vol. 27, page 121 (191 6). 



CHAPTER IX 

INORGANIC FOODSTUFFS AND THE MINERAL 
METABOLISM 

The Elementary Composition of the Body 

From various estimates by different writers the average ele- 
mentary composition of the human body may be presumed to 
be approximately as follows : 

Oxygen, about 65. per cent 

Carbon, about 18. pier cent 

Hydrogen, about 10. per cent 

Nitrogen, about 3. per cent 

Calcium, about 2. per cent 

Phosphorus, about i. per cent 

Potassium, about 0.35 per cent 

Sulphur, about 0.25 per cent 

Sodium, about 0.15 per cent 

Chlorine, about 0.15 per cent 

Magnesium, about 0.05 per cent 

Iron, about 0.004 per cent 

Iodine "j f Very 

Fluorine > { minute 

Silicon J [ quantities 

Traces of some other elements such as manganese and alumin- 
ium may perhaps be normal constituents of the body also, and 
even arsenic has been discussed as a possible essential element. 
In this book only those elements are discussed of which the 
amounts concerned in daily metaboHsm can be measured quan- 
titatively by present methods. 

Since all of the substances in the body are continually under- 
going disintegration and renewal, it follows that there must be 

234 



INORGANIC FOODSTUFFS AND MINER.AL METABOLISM 235 

a constant metabolism or exchange of every element which enters 
into body structure. More or less of each element must each 
day be metabolized and eHminated ; and, if equilibrium is to be 
maintained, an equal amount must be supplied. 

Simple proteins furnish only five of the fifteen chemical ele- 
ments which are known to be essential to human nutrition, 
while fats and carbohydrates are composed of but three of these 
five. Ten of the fifteen essential elements, or seven of the 
twelve which are essential in amounts sufficiently large to be 
measurable by present methods, must therefore be furnished 
by some ingredients of the intake other than simple proteins, 
fats, and carbohydrates. These same elements are found to 
remain either wholly or largely in the ash of food materials when 
the latter are burned in tne air ; and when the food is metab- 
olized in the body they are excreted chiefly in the form of 
mineral matter. These elements are therefore grouped as " ash 
constituents," " minerals," " mineral salts," " inorganic ele- 
ments," or " the inorganic foodstuffs " ; and their metabohsm 
is commonly designated as " the mineral metabohsm." None 
of these terms is entirely appropriate. To designate the ele- 
ments which remain in the ash when food is burned as ash con- 
stituents is accurate but not very instructive, since the materials 
of which a food ash is composed may have existed in quite dif- 
ferent forms of combination in the food before it was burned. 
The terms " mineral " and " inorganic " are likely to be some- 
what misleading. Some of the elements (as sodium and chlo- 
rine) do exist in the food and enter and leave the body in in- 
organic forms ; others (as iron and sulphur) exist in the food 
and function in nutrition as essential constituents of organic 
matter and become inorganic only as the organic matter is oxi- 
dized, i.e. only in the late stages of their metabolism ; still 
others (as phosphorus) are supplied to the body by the food in 
both organic and inorganic forms. 

The elements concerned in " the mineral metabolism " may 



236 CHEMISTRY OF FOOD AND NUTRITION 

exist in the body and take part in its functions in at least three 
kinds of ways : 

(i) As bone constituents, giving rigidity and relative per- 
manence to the skeletal tissues. 

(2) As essential elements of the organic compounds which 
are the chief solid constituents of the soft tissues (muscles, 
blood cells, etc.). 

(3) As soluble salts (electrolytes) held in solution in the fluids 
of the body, giving these fluids their characteristic influence 
upon the elasticity and irritability of muscle and nerve, supply- 
ing the material for the acidity or alkalinity of the digestive 
juices and other secretions, and yet maintaining the neutrality 
or slight alkalescence of the internal fluids as well as their 
osmotic pressure and solvent power. 

A man under average conditions of diet, activity, and health 
usually excretes daily from 20 to 30 grams of mineral salts, 
consisting essentially of chlorides, sulphates, and phosphates of 
sodium, potassium, magnesium, and calcium (as well as am- 
monium salts from the protein metabolism). 

The purpose of this chapter and the one following is to 
sketch briefly the metaboHsm of these substances, with a 
more detailed quantitative study of the three elements (cal- 
cium, phosphorus, and iron) which assume an especial promi- 
nence in the practical problems of nutrition. 

Metabolism of Chlorides — Use of Common Salt 

Except for the hydrochloric acid of the gastric juice, prac- 
tically all the chlorine involved in metabolism enters, exists in, 
and leaves the body in the form of chlorides — much the greater 
part as sodium chloride. The amount of sodium chloride which 
is ordinarily added to food as a condiment is so large that the 
amounts of sodium and chlorine present in the various foods in 
the fresh state become of little practical consequence. Among 
animals the herbivora require salt while the carnivora do not, 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 237 

the latter obtaining sufficient salt for their needs from the flesh, 
and more especially from the blood, of their prey. 

Sodium occurs, chiefly as chloride, abundantly in the blood 
and other fluids of the animal body and in much lower concen- 
tration in the tissues. Potassium, on the other hand, occurs 
to a greater extent as phosphate than as chloride. It is most 
abundant in the soft solid tissues — in the corpuscles of the 
blood, the protoplasm of the muscles, and other organs, and 
also in the highly speciaHzed fluids which some of the glandular 
organs secrete, notably in milk. Since the cells arc in constant 
contact with the circulating fluids, the abundance of potassium 
in the cells and of sodium in the fluids makes it evident that 
the taking up of salts by the cells is an active or " selective " 
process. A conspicuous function of the salts in the tissues is 
the maintenance of the normal osmotic pressure, but solu- 
tions of different salts of equal osmotic pressure are by no 
means interchangeable, and it is not possible to replace suc- 
cessfully the potassium in the cell by an equivalent amount 
of sodium. 

There ^eems to be a relation between the taking up of salt 
and the retention of water in the tissues. The effect of decreas- 
ing the salt in the diet is to decrease the quantity of salt in the 
tissues, and at the same time their water content. An explana- 
tion of this Ues in the fact that, since body tissues and fluids 
must maintain a constant concentration of sodium chloride, a 
reduction in the absolute quantity of salt must result in a cor- 
responding reduction in the quantity of water present. 

Attention is frequently called to the fact that sodium chloride 
is the only salt which we seem to crave in greater quantities 
than occur naturally in our food, and that we share this appetite 
with the herbivorous animals. Bunge holds that this is because 
a high intake of potassium (as in most vegetable foods) tends 
to increase sodium elimination. Bunge tested this theory upon 
his own person by taking 18 grams of potash (as phosphate and 



238 CHEMISTRY OF FOOD AND NUTRITION 

citrate) in one day. This increased the eUmination of sodium 
chloride by 6 grams. 

In his Physiological and Pathological Chemistry (Chapter 
VII), Bunge records extended and interesting observations and 
discussion upon the relation of diet to the craving for salt, and 
concludes that while one might Hve without the addition of 
salt to the food even on a diet largely vegetarian, yet without 
salt we should have a strong disinclination to eat much of the 
vegetables rich in potassium, such as potatoes. " The use of 
salt enables us to employ a greater variety of the earth's prod- 
ucts as food than we could do without it." But also, accord- 
ing to Bunge : " We are accustomed to take far too much salt 
with our viands. Salt is not only an aliment, it is also a condi- 
ment, and easily lends itself, as all such things do, to abuse." 
While Bunge's explanations may not be entirely adequate in 
detail, there seems to be little doubt as to the correctness of his 
main deductions. 

Since the sodium chloride taken with the food passes through 
the body and is excreted by the kidneys without undergoing 
any chemica' change, the rate of excretion quickly adapts itself 
to the rate of intake within wide variations. 

When no chloride is taken, the rate of excretion falls rapidly 
to a point where the daily loss is only a very small fraction of 
the amount ordinarily consumed and excreted. Thus in an 
experiment by Goodall and Joslin * in which a healthy man 
was placed upon a diet adequate in protein and energy value 
but practically free from salt, the excretion of chlorine on each 
of 13 successive days was respectively: 4.60, 2.52, 1.88, 0.87, 
o.6g, 0.48, 0.46, 0.40, 0.26, 0.22, 0.22, 0.17, 0.17 grams. 

Cetti in ten days of fasting excreted all together 13.13 grams, 
and BelH in ten days on a diet poor in salt lost 11.8 grams of 
sodium chloride. In Benedict's recent study of prolonged fast- 

* Goodall and Joslin, Transactions oj the Association of American Physicians, 
Vol. 23, page 92 (1908). 



INORGANIC FOODSTUFFS AND MINER.\L METABOLISM 239 

ing * his subject lost 8.44 grams of chlorine (equivalent to 13.93 
grams sodium chloride) during the first ten days, 2.13 grams 
chlorine during the second ten days, and 1.57 grams chlorine 
during the third ten days of the fast. (The detailed data may 
be found on a later page.) Since the body is supposed to con- 
tain about 100 grams of sodium chloride, it will be seen that 
even when there was complete deprivation of salt for ten to 
thirty days, the total losses did not exceed 10 to 20 per cent of 
the amount estimated as usually present in the body. The 
salt thus readily given off by the body has been regarded by 
some as a measure of the excess which the body has been forced 
to carry in consequence of the extravagant amounts of salt 
which are commonly taken with the food. Magnus-Levy, how- 
ever, thinks that the reduced amount of sodium chloride left in 
the body after such a loss is " not a physiological optimum, but 
rather a physiological minimum." 

Moderate variations in the amount of salt taken have no 
significant effect upon metabolism. Large amounts increase the 
quantity of protein cataboHzed, and, through overstimulating 
the digestive tract, may also interfere with the absorption and 
utilization of the food. 

Metabolism of Sulphur 

Plants absorb sulphates from the soil and use the sulphur in 
the synthesis of proteins. Minute quantities of inorganic sul- 
phates may be taken by man in food and drink, but by far the 
greater part of the sulphur concerned in metabolism enters the 
body in organic combination and, so far as known, chiefly as 
protein. The metabolism of sulphur is therefore a part of the 
protein metaboHsm, and in many respects the metabolism of 
sulphur tends to run parallel with that of nitrogen. In a 
series of ten experiments (each of 3 to 5 days' duration) upon 

* Benedict, Publication No. 203, Carnegie Institution of Washington. 



240 



CHEMISTRY OF FOOD AND NUTRITION 



man,* in which the food consisted of bread and milk in varying 
amounts and proportions, the percentage absorption from the 
digestive tract was nearly the same for the sulphur as for the 
nitrogen of the food, and the excretion of the end products ran 
so closely parallel that in every case in which the body stored 
nitrogen it also stored sulphur, and vice versa. f 

It is well known that individual proteins show relatively 
much greater differences in sulphur than in nitrogen content, so 
the ratio of nitrogen to sulphur varies widely, as is shown by 
the following examples selected from the data for pure proteins 
compiled by Osborne : 



Kind of Protein 



Legumiri . . 

Zein . . . . 

Edestin . . . 

Gliadin . . . 

Leucosin . . 

Casein . . . 

Myosin . . . 
Serum globulin 

Egg albumin . 



Nitrogen 
Per Cent 



18.04 
16.13 
18.69 
17.66 
16.80 
15-78 
16.67 
15-85 
15-51 



SULPHDR 

Per Cent 



0.385 

0.600 

0.88 

1.027 

1.280 

0.80 

1.27 

I. II 

1.616 



Ratio of Nitro- 
gen TO Sulphur 



46.9 
26.9 
21.2 
17.2 

13-1 
19.7 

I3-I 

14-3 

9.6 



Thus, while many proteins approximate the usually assumed 
average of 16 per cent nitrogen and i per cent sulphur, there 
are considerable deviations from this ratio in both directions. 

Under ordinary conditions, however, no protein is eaten in a 
pure state, but only as the material containing it is used as an 
article of food. It is therefore the proportion of sulphur to the 
total protein of the food which determines the ratio of sulphur 
to nitrogen available for nutrition. 

♦Bulletin 121, Office of Experiment Stations, U. S. Department of Agriculture. 
t Exceptions to such parallelism of nitrogen and sulphur balances have, however, 
been reported in certain pathological conditions. 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 241 

The proportion of sulphur to total protein has been deter- 
mined in most staple foods, of which the following are repre- 
sentative : * 



Food Material 


SuLPHUK IN Percentage of 
Total Protein 


Lean beef 


0.95-1.00 

1.4 
0.95-1.09 
I.15-1.29 

1.30 

1-55 
0.69-1.00 
0.80-0.94 

1.07 


Eggs 

Milk 


Wheat flour, crackers 

Entire wheat 


Oatmeal 

Beans 

Peas 


Potatoes 



Taking these figures as typical, it would appear that in those 
staple foods which contribute the greater part of the protein of 
the diet, the ratio of protein to sulphur does not differ greatly, 
and that in most cases of ordinary mixed diet there would be 
consumed not far from i gram of sulphur in each 100 grams of 
protein. We may therefore expect that in health and on an 
ordinary diet the sulphur requirement will usually be covered 
when the protein supply is adequate. 

When proteins (or their cleavage products) are oxidized in 
the body, the sulphur becomes converted for the most part into 
sulphuric acid, which, of course, must be neutralized as rapidly 
as it is formed. The greater part of the sulphuric acid formed 
in metabolism appears in the urine as inorganic sulphates ; a 
smaller part is found combined with organic radicles in the form 
commonly known as " ethereal " or " conjugated " sulphates. 
The amount of ethereal sulphate or the ratio of ethereal to in- 
organic sulphate is quite variable, depending mainly upon the 

* In the data here given, nitrogen and sulphur were determined in the same 
specimens. Average percentages of protein and sulphur in nearly all important 
food materials may be found in Tables I and II, respectively, of the Appendix. 
R 



242 CHEMISTRY OF FOOD AND NUTRITION 

amount and character of the intestinal putrefaction, which in 
turn is apt to be considerably influenced by the food. On ordi- 
nary mixed diet about one tenth or one twelfth of the sulphate 
sulphur in the urine ordinarily appears as ethereal sulphates; 
but when the meat in the diet is replaced by milk, the putre- 
faction is usually lessened and the proportion of ethereal sul- 
phates lowered. In one case of a healthy man who had been 
on a bread and milk diet for a week, only one thirtieth of the 
sulphate sulphur was in the form of ethereal sulphates. 

Not all of the metabolized sulphur is eliminated as mineral 
or " ethereal " sulphate ; a part is given off in less completely 
oxidized forms. This " unoxidized " or " neutral " sulphur 
usually constitutes in healthy persons on full diet from 5 to 15 
per cent of the total sulphur eliminated. In Folin's experiment 
upon very low protein diet, although the total sulphur metab- 
olism was markedly decreased, the quantity of neutral sulphur 
excreted remained about constant, so that the relative proportion 
of sulphur appearing in this form was increased. 

Metabolism of Phosphorus 

Phosphorus compounds are as widely distributed in the body 
and as strictly essential to every living cell as are proteins. 

Phosphates are constantly excreted from the body even after 
long fasting. During a fast the rate of excretion of phosphates 
does not fall off rapidly like that of chlorides, but tends to run 
more nearly parallel with the nitrogen excretion, as would be 
expected in view of the fact that the phosphates of the urine 
represent not only an excretion of preexistent salts, but also the 
result of the metabolism of body tissue. 

Some of the relations of the phosphorus compounds to nutri- 
tional functions are outlined by Forbes and Keith as follows : 

" Among the several inorganic elements involved in animal 
life phosphorus is of especial interest. No other one enters 
into such a diversity of compounds and plays an important 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 243 

pari in so many functions. Structurally, it is important as a 
constituent of every cell nucleus and so of all cellular structures ; 
it is also prominent in the skeleton, in milk, in sexual elements, 
glandular tissue, and the nervous system. Functionally, it is 
involved in all cell multiplication, in the activation and control 
of enzyme actions, in the maintenance of neutrality in the 
organism, in the conduct of nerve stimuli, and through its rela- 
tion to osmotic pressure, surface tension, and imbibation of 
water by colloids it has to do with the movement of liquids, 
with the maintenance of proper liquid contents of the tissues, 
with cell movements, and with absorption and secretion " 
(Ohio Agricultural Experiment Station, Technical Bulletin No. 
5, page 11). 

While the phosphorus compounds of the body and of the food 
are very^numerous and might be classified differently according 
to the standpoint from which they are being considered, it will 
be convenient for our present purposes to divide them into four 
main groups : 

1. Inorganic phosphates, of which potassium phosphate is 
probably the most abundant in food and in the fluids and soft 
tissues of the body, while calcium phosphate is the chief inorganic 
constituent of bones. 

2. Phosphorus-containing proteins, including the nucleo- 
proteins of cell nuclei, the lecitho-proteins, and the true phos- 
phoproteins such as casein or caseinogen of milk and ovovitellin 
of egg yolk. 

3. Phosphatids, phospholipins or phosphorized fats — includ- 
ing lecithins, lecithans, kephalins, etc. — which occur in large 
quantity in brain and nerve tissue and in smaller concentra- 
tion (but probably as essential components) in all the cells and 
tissues of the body, not only of man, but of plants and animals 
generally. The phosphatids are therefore widely distributed in 
food materials, but are found in extremely varying proportions 
in foods of different types. Egg yolks are conspicuously rich 



244 CHEMISTRY OF FOOD AND NUTRITION 

in phosphatids, about two thirds of the phosphorus of the egg 
being present in this form. 

4. Phosphoric acid esters of carbohydrates and related sub- 
stances such as inositol (" inosite ") and the natural salts of 
such esters. The calcium, magnesium, and potassium salts of 
" phytic acid," * collectively known as phytates, phytins, or 
phytin, have for some years been regarded as the most abundant 
phosphorus compounds of the wheat kernel and probably of 
the grains and legumes generally, if not of all vegetable foods. 
Recent investigations indicate, however, that not all the phos- 
phorus compounds which were supposed to be phytins are really 
salts of phytic acid. As has been explained in Chapter I, the 
recent work of Northrup and Nelson indicates that starch con- 
tains phosphorus as an essential constituent, and there are other 
indications of phosphorus-containing carbohydrates or carbo- 
hydrate-phosphoric acid esters in food materials and also of the 
formation of hexose-phosphoric acid esters in the body in the 
course of the carbohydrate metaboHsm. 

Thus we may think of the phosphorus with which we have 
to deal in food and nutrition as being partly in the form of in- 
organic phosphates and partly in combination with (or present 
as a constituent of) each of the three groups of organic food- 
stuffs — proteins, fats, and carbohydrates, or closely related 
substances. 

In the course of digestion and metabolism the phosphoric 
acid radicles are split off from the organic radicles and ulti- 
mately nearly all of the phosphorus leaves the body as inorganic 
phosphate. To what extent the cleavage of the organic phos- 
phorus compounds occurs in the digestive tract under ordinary 
conditions and to what extent, if at all, the phosphorus of phos- 
phoproteins or phosphatids, for example, is absorbed in organic 
form is still a subject of investigation. 

* Phytic acid is probably inositol-hexa-orthophosphoric acid, CsHziOjiPe (Rob- 
inson and Mueller). 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 245 

Interrelations of Phosphates, Phosphoproteins, and 
Phosphatids 

Phosphates, nucleoproteins, and phosphatids are all promi- 
nent as body constituents. 

The insoluble phosphates constitute the chief mineral matter 
of bone ; while soluble phosphates are essential constituents of 
the blood and protoplasm. It is largely to the presence of the 
phosphates that the blood and protoplasm owe their ability to 
remain neutral or faintly alkaline, notwithstanding the constant 
production of acid in metabolism, as will be seen in connection 
with the discussion of the maintenance of neutrality below. 

The nucleoproteins as constituents of cell nuclei and the phos- 
phatids as prominent constituents of brain and nerve tissue and 
as less prominent but doubtless essential components of the 
tissues generally have functions distinct from each other and 
from the phosphates. On the assumption of a more active 
metaboHsm in the cell nuclei or in the brain and nerve tissue 
than in the bones, there has sometimes been a tendency to regard 
fluctuations of phosphorus output as indicative of increased or 
decreased metabolism of nucleoproteins or phosphatids. It is 
probable, however, that the eliminated phosphorus represents 
more largely material which has functioned as phosphate. One 
reason for this is that the bones contain so large a share of the 
total phosphorus of the body. According to Voit's estimate, a 
man's skeleton contains about 600 grams of phosphorus; his 
muscles, about 56 grams ; his brain and nerves, about 5 grams. 
With the bones in possession of such a predominant share of 
the body phosphorus, it would seem that the metabolism of 
bone tissue, even though relatively inactive, must exert a con- 
siderable influence upon the phosphorus output. Moreover, 
the soluble phosphates of the blood and protoplasm are con- 
stantly tending to be eliminated from the body (through the 
kidneys or the intestinal walls or both) and perhaps increasingly 



246 CHEMISTRY OF FOOD AND NUTRITION 

so in proportion as ihcy become changed into acid phosphates 
in the performance of their function of maintaining neutrality 
by reacting with the acids produced in metai)olism. Before 
taking up the quantitative study of the phosphorus requirement 
we must consider the nutritive relations of the diflerent t^q^es 
of phosphorus compounds, and whether these are sufBciently 
interchangeable in nutritive function so that one may properly 
speak of phosphorus requirement, simply, \\dthout discriminating 
between phosphates, phytates, phosphoproteins, and phosphatids. 

Such experimental evidence as is cited here will be given in 
general in chronological order, to indicate, if possible, how pres- 
ent \'iews have actually developed, and to suggest that they 
may at any time require modification as a result of further 
research. 

Meischer studied the formation of complex from simpler phos- 
phorus compounds in the adult animal body by observations 
upon the Rhine salmon, which during the breeding season re- 
main a long time in fresh water, taking no food, but developing 
large masses of roe and milt at the expense of muscular tissue. 
This process evidently involves the formation of considerable 
amounts of nucleoproteins and phosphatids from simpler pro- 
teins, fats, and phosphorus compounds of the muscles. Paton * 
has studied the salmon of Scotland with similar results. Is there 
then any advantage in feeding phosphorus in organic forms? 

Marcuse,t followed by Steinitz,J Zadik, § and Leipziger, || 
studied, by metabolism experiments on dogs, the nutritive value 
of phosphoproteins, when fed to the exclusion of phosphates 
and when contrasted with equivalent amounts of phosphorus 
and nitrogen fed in the form of mixtures of inorganic phosphates 
and simple proteins. Casein and ovovitellin were taken as 

* Journal of Physiology, Vol. 22, page 333. 

t Archiv Jiir die gesammle Physiologic (I^fluger), Vol. 67, page 373. 

X Ibid., Vol. 72, page 75. § Ibid., V'ol. 77, page i. 

II Ibid., Vol. 78, page 402. 



INORGANIC FOODSTUFFS AND illNERAL METABOLISM 247 

typical phosphoproteins and compared with either myosin or 
edestin fed with inorganic phosphates. Rohmann * summarized 
the results as a whole and found a striking difference in the phos- 
phorus balances in favor of the phosphoproteins as against the 
mixtures of simple proteins with inorganic phosphates. The 
storage of nitrogen was also more pronounced in the periods in 
which the phosphorized proteins were fed. The results appear 
to justify Rohmann's conclusion that the nutritive values of 
phosphorized and phosphorus-free proteins are not entirely the 
same, the former being especially adapted to furnish the material 
for tissue growth. 

In experiments upon men, Ehrstrom f and Gumpert J have 
found that a smaller amount of phosphorus will maintain phos- 
phorus equilibrium when taken in the form of casein than when 
taken largely as dicalcium phosphate or as meat, the phosphorus 
of which is largely in the form of potassium phosphate. On the 
other hand Keller § in a study of the phosphorus metabolism of 
young children found evidence that storage of phosphorus was 
favored by food (like milk) which contained a liberal supply of 
phosphates in addition to the organic phosphorus compounds; 
and Von Wendt found that the loss of phosphorus occurring on 
a diet very poor in ash could be greatly reduced by the addition 
of dicalcium phosphate to the food. 

In cow's milk the greater part of the phosphorus appears to 
exist as phosphate, but there can be no doubt that the milk 
phosphorus as a whole is available for the needs of the young 
of the species, especially in view of the parallelism pointed out 
by Bunge and Abderhalden between the phosphorus and cal- 
cium content of milk and the rate of growth of the young. (See 
accompanying table.) 

* Berlin klinische Wochensckri/l, Vol. 35, page 78g. 

"I" Skandinavisches Archiv fiir Physiologic, \o\. 14, page 82. 

X Medische Klinik, Vol. i, page 1037. 

§ Archiv J Ur KinderheUkunde, Vol. 29, page i. 



248 



CHEMISTRY OF FOOD AND NUTRITION 







No. OF Days 
Required to 
Double the 
Birth Weight 


Percentage Composition of Milk (Partial) 


Spectes 


Protein 


Ash 


Calcium 


Phosphorus 


Human 

Horse 

Cow 

Goat 

Sheep 

Swine 

Dog 

Rabbit 










1 80 
60 

47 
22 

15 

14 

9 

6 


1.6 

2.0 
3-5 
3-7 
4-9 

5-2 

7-4 
14.4 


0.2 
0.4 

0.7 
0.78 
0.84 
0.80 

1-33 
2.50 


0.02 
0.09 
0.12 
0.14 
0.18 
0.18 
0.32 
0.65 


0.02 
0.06 
0.09 
0.18 

O.II 

0.14 
0.22 
0-43 



It is, however, not without possible significance that the phos- 
phorus of human milk is mainly in organic forms (Soldner) and 
that, notwithstanding its much lower content of total phos- 
phorus, human milk contains as high a percentage of lecithin 
as does cow's milk (Stoklasa). An infant fed on diluted cow's 
milk must therefore receive less lecithin than the breast-fed 
infant while it may receive more total phosphorus. 

In general the more recent investigations favor the view that 
the body can use inorganic phosphates to meet all its phosphorus 
requirements. 

Hart, McCollum, and Fuller showed in 1909 that with young 
pigs on a ration too poor in phosphorus to support normal growth 
the deficit could be made good by feeding phosphates as well as 
by feeding foods containing organic phosphorus compounds. 

The following year (1910) McCollum reported that, other 
things being satisfactory, all the phosphorus requirements of an 
animal can be met by feeding inorganic phosphates. In one of 
these experiments McCollum kept a rat for 104 days on diets 
of purified food materials in which phosphorus was given only 
as phosphate. It maintained good condition but suffered some 
loss of weight as it would not eat enough of the artificial food 
to meet the energy requirement. In another case in which an 
amino acid mixture from the hydrolysis of beef muscle was 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 249 

added to the diet the food was eaten more readily and one rat 
increased in weight from 153 to 176 grams while receiving only 
inorganic phosphorus. 

As young rats eat unpalatable food more readily than do 
adults, McCollum fed the ration containing phosphate as sole 
source of phosphorus to young growing rats, one of which ate 
the ration for 127 days, during which time he doubled in weight. 
At the end of this experiment the rat was killed and analyzed 
and found to be of normal composition. There was therefore 
no reason to doubt that the rat synthesized the nucleoproteins 
and phosphatids of his growing tissues from the inorganic phos- 
phorus of his food. 

Subsequent experiments by McCollum and Davis, as well as 
those of Osborne and Mendel described in connection with the 
discussion of proteins (Chapter III), afford many instances of 
long-continued growth of rats on rations made up of " isolated " 
foodstuffs in which all or nearly all of the phosphorus was in 
the form of simple phosphates. 

In order to determine whether the synthesis of lecithin in the 
animal body can be demonstrated experimentally, McCollum, 
Halpin, and Drescher (191 2) fed 3 hens for 10 weeks a ration 
consisting of 30 per cent skim milk powder and 70 per cent 
polished rice, both of which were freed from phosphatids. This 
diet it will be noted contained phosphoprotein as well as phos- 
phate, but very little fat, and it was believed no phosphatid. 
The hens produced eggs in normal number and of normal com- 
position. The phosphatid in the eggs produced was 27.65 grams 
per hen, and this was behaved to have been synthesized rather 
than to have come from material previously stored. 

Fingerhng (191 2) kept ducks for 8 months on a diet of pota- 
toes, blood albumin, starch, and lime salts. The ducks laid 
normally and the phosphatid content of the eggs produced was 
determined. Since the phosphatid content of the food must 
have been small and the feces always contained some lecithin- 



2 50 CHEMISTRY OF FOOD AND NUTRITION 

like substances, and since the ducks did not lose weight, Finger- 
ling concludes that the organic phosj^horus compounds in the eggs 
were synthesized from inorganic phosphorus obtained in the food. 

Later he fed the same ducks on food richer in organic phos- 
phorus ; and as they produced about the same number of eggs 
of similar phosphatid content he concluded that the egg-phos- 
phatids were synthesized as readily from inorganic as from 
organic phosphorus compounds. 

The evidence seems sufficient to warrant the statement that 
animal organisms are able to synthesize nucleoproteins, phospho- 
proteins, and phosphatids from inorganic phosphate. It may, 
however, still be questioned whether the nutritive conditions 
are as favorable when the body is forced to do this as when a 
part at least of the phosphorus reciuirement is met by feeding 
phosphoproteins and phosphatids. 

The above-mentioned experiments of Rohmann and his 
pupils on dogs and of Ehrstrom and Gumpert on men seemed 
to demonstrate that the phosphoproteins have a higher food 
value than a corresponding mixture of simple proteins and simple 
phosphates ; and the recent feeding experiments, while showing 
the efficiency of phosphates in meeting the phosphorus require- 
ment, do not show conclusively that the phosphates are of fully 
equal value with the organic phosphorus compounds. Feeding 
experiments of long duration are well fitted to give convincing 
evidence on the former point, but are not so well suited for the 
purposes of exact quantitative comparisons because the very 
fact of their long duration gives opportunity for other factors to 
enter, such as differences in vitality among the experimental 
animals. Masslow, as the result of recent investigation of 
phosphorus metabolism during growth, holds (1913) that for 
the best results a considerable part of the phosphorus should 
preferably be supplied in organic forms. 

Some writers have argued that the presence in extracts of 
intestinal mucosa of enzymes capable of splitting off phosphoric 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 25 1 

acid from the organic phosphorus compounds of the food may 
be taken as evidence that phosphorus is absorbed as phosphoric 
acid or phosphate whatever the form in which it occurs in the 
food ; but in view of the reversibihty of enzyme action and the 
great extent to which it is influenced by conditions, it seems pref- 
erable to form our impressions regarding the equivalence or 
relative values of the different phosphorus compounds from 
observations or experiments upon animals rather than from 
tests for enzymes in tissue extracts. 

Forbes holds that even though the phosphorus be absorbed 
as inorganic phosphate there is advantage in having it supplied 
largely in organic . forms since " much larger amounts of phos- 
phorus may be utilized in a normal manner if they are gradually 
liberated in the usual way by the digestive cleavage of the 
organic complexes with which they are combined." * 

Forbes and Keith (1914) after reviewing most thoroughly 
the whole literature of phosphorus compounds in animal metab- 
olism, draw, among others, the following conclusion : 

" That organic phosphorus is absolutely essential to any 
animal has not been demonstrated. The proof that inorganic 
phosphorus can serve all of the purposes for which any animal 
needs phosphorus is incomplete.! There is much evidence to 
imply that, with some species at least, some organic phosphorus 
compounds are more useful than is inorganic phosphorus in the 
sense of being more readily and economically utihzed, and of 
maintaining a higher state of vitahty as revealed by tissue 
enzyme estimations, the difference probably depending, in part 
at least, on the fact of the partial absorption and utilization of 
organic phosphorus compounds as such, without complete diges- 
tive cleavage " (Ohio Agricultural Experiment Station, Tech- 
nical Bulletin No. 5, pages 364-365). 

^= Ohio Agricultural Experiment Station, Technical Bulletin No. 5, page 357. 
t (Some of the experiments of Osborne and Mendel and of McCollum and Davis 
have appeared since the above was written by Forbes and Keith. H. C. S.) 



252 CHEMISTRY OF FOOD AND NUTRITION 

On the other hand Marshall * considers the evidence fully 
sufficient to warrant the conclusion that organic phosphorus 
compounds are of no more value as food than are the inorganic 
phosphates. 

In the present state of our knowledge there is at least no 
quantitative measure of differences in nutritive value as between 
different forms of phosphorus. If differences in nutritive value 
between the different groups of phosphorus compounds exist, 
they are doubtless in favor of the phosphoproteins and phos- 
phatids and are more significant for the growing than for the 
full-grown organism. For the reasons explained in Chapters 
VIII, XIII, and XIV the diet of growing children should 
always contain a Hberal allowance of milk. The milk will pro- 
vide, in addition to the best form of protein, a high proportion 
of phosphoprotein and also significant quantities of phosphatids. 
Hence it seems justifiable to assume that, if the food is properly 
selected, one may compute its total phosphorus content and 
compare it with the total phosphorus requirement of the body 
without separate computation of the different forms of phos- 
phorus. 

Estimation of the Phosphorus Requirement 

Since phosphorus compounds are essential to all the tissues 
of the body, the growth of new tissue requires a storage of 
phosphorus along with that of protein, but aside from this it is 
evident that the phosphorus metabolism presents a separate 
problem from the metabolism of protein. 

The phosphorus of the tissues exists largely in the form of 
nucleoproteins — the characteristic substances of cell nuclei 
— and, as these are important in metabolism, there was a 
tendency for a number of years to regard the phosphorus elim- 
ination as largely a measure of the metabolism of nucleo- 
proteins somewhat as the nitrogen is taken as a measure of the 
* Journal of the American Medical Association, Vol. 64, page 573 (1915). 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 253 

metabolism of proteins in general. It is probable, however, 
that such a view of the phosphorus metabolism is of only very 
Hmited application, because of the influence of other factors. 
Voit showed that the material metabolized in fasting comes 
largely from the bones. Undoubtedly the bones take part in 
the daily metabolism, and while they may undergo a less active 
exchange of material than the soft tissues, they possess such a 
large proportion of the phosphorus in the body that they prob- 
ably contribute a considerable part of what is metabolized from 
day to day. Moreover, recent investigations upon the func- 
tion of the soluble phosphates of the blood in maintaining neu- 
trahty in the body indicate that the neutralization of acid by 
conversion of di- into mono-phosphates may be followed by an 
increased excretion of the acid phosphate in the urine. Finally, 
it is evident that the amount of phosphorus metaboHzed is 
very directly influenced by the amount taken in the food. 

The phosphorus which has been metabohzed is excreted from 
the body almost entirely in the form of inorganic phosphates, 
the organic phosphorus of the urine constituting as a rule only 
I to 3 per cent of the total.* Carnivorous animals excrete phos- 
phates mainly through the kidneys, but in the herbivora the 
excretion occurs almost entirely through the intestinal wall, 
whether the phosphate be taken by the mouth, or injected sub- 
cutaneously, or be formed by metabolism of organic phosphorus 
compounds in the body. In man, the ehmination of metab- 
olized phosphorus is partly through the kidneys and partly 
through the intestinal wall, the relative quantities in urine and 
feces varying within rather wide hmits. As a rule, foods rich 
in calcium, or which yield an alkaline ash, tend to increase the 
proportion of phosphorus excreted by way of the intestine. 

Attempts have sometimes been made to estimate the phos- 
phorus requirement from the amount excreted in the urine. 

* Some investigators have doubted the occurrence of organic phosphorus in urine 
while others have estimated it as high as 6 per cent of the total urinary phosphorus. 



254 



CHEMISTRY OF FOOD AND NUTRITION 



The results thus obtained are always too low (usually very much 
so), and are largely responsible for the fact that the amount of 
phosphorus required for the normal nutrition of man is seriously 
underestimated in many of the standard textbooks. 

Since the excretion of metabolized phosphorus through the 
intestine is in man too large to be neglected and too variable to 
be allowed for by calculation, we can expect reliable data on 
phosphorus requirements from those experiments only in which 
the amounts of phosphorus are actually determined in food, in 
feces, and in urine. In such experiments it is found (as in the 
case of nitrogen) that the output obtained upon the experi- 
mental days is influenced not only by the food taken at the 
time, but also by the rate of metabolism to which the body had 
been accustomed on the preceding days. This is shown by the 
following results obtained in a 12-day series of experiments 
upon a healthy man: 



Phosphorus Metabolism ^\^TH Different Amounts of Phosphorus 

IN THE Food 



Experimental Period 


Phosphorus per Day 


No. 


Duration 


In Food 
Grams 


In Feces 
Grams 


In Urine 
Grams 


Output 
Grams 


Balance 
Grams 


I 

II 

III 


3 days 
6 days 
3 days 


0.40 
0.77 
I-5I 


0.45 

O.IQ 
0.50 


0.70 
0.72 
0.99 


I-I5 
0.91 
1.49 


- 0-75 

- 0.14 
-}- 0.02 



Here the output of phosphorus was greater in the first period 
with 0.40 gram in the food than in the second when the food 
furnished 0.77 gram, probably because the first period followed 
and was influenced by a preceding diet fairly rich in phosphorus, 
whereas the output in Period II was influenced by the low- 
phosphorus diet of Period I. For the same reason Period II 
offered favorable conditions for the establishment of equilibrium 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 255 

on a minimum diet, and the results show that in this case the 
subject was unable to reach equilibrium on 0.77 gram per day, 
the output averaging 0.91 gram. When the intake was in- 
creased to 1. 5 1 grams, the output rose rapidly and averaged 
1.49 grams. In this case the amount which would have been 
just sufficient for equilibrium evidently lay between 0.91 and 
1.49 grams per day. By means of well-planned experiments or 
series of experiments it is possible to fix for a given individual 
much narrower limits within which the exact amount required 
for equilibrium must lie, and when it is known that the intake 
approximates this required amount, it is justifiable to regard 
the output as an indication of the normal nutritive requirement. 
Study of the data of 93 such phosphorus balance experiments 
upon 27 subjects, 21 men and 6 women, has shown a range of 
0.52 to 1.75 grams with an average of 0.96 gram phosphorus 
(2.20 grams PoOs) per 70 kilograms of body weight per day. 
This corresponds with the average requirement of 50 grams 
protein per day per man of 70 kilograms as estimated on page 
220. Allowing 50 per cent above the bare minimum would give 
a phosphorus " standard " of 1.44 grams (3.30 grams P2O5) 
corresponding to a protein " standard " of 75 grams. 

Phosphorus in Food Materials and Typical Dietaries 

A comparison of the amounts of phosphorus contained in the 
food of typical American famihes with the amounts metabohzed 
in the experiments above mentioned indicates that a freely 
chosen diet does not always furnish an abundance of phosphorus 
compounds. In 150 American dietaries of families or larger 
groups believed to be fairly representative, the estimated amount 
of phosphorus furnished per man per day was below 0.96 gram 
in 7 cases, while in no case was there less than 50 grams of pro- 
tein per man per day. If we allow a margin of 50 per cent for 
safety in both protein and phosphorus, we find 8 per cent of the 
dietaries below the protein standard of 75 grams and 41 per 



256 CHEMISTRY OF FOOD AND NUTRITION 

Approximate Amounts of Phosphorus in Food Materials 



Food 


Phosphorus 

PER 100 Grams 

Edible Substance 


Phosphorus 

per 100 Graus 

Protein 


Phosphorus 
per 3000 
Calories 


Beef, all lean 

Eggs 

Egg yolk 

Milk 

Cheese 

Wheat, entire grain . . . 
White flour 

Rice, polished .... 

Oatmeal 

Beans, dried 

Beets 

Carrots 

Potatoes 

Turnips 

Apples 

Bananas 

Oranges 

Prunes, dried 

Almonds 

Peanuts 

Walnuts 


0.218 

.180 

•524 

•093 
.683 

•423 
.092 

.096 

•392 

.471 
•039 
.046 
.058 
.046 

.012 

■031 
.021 
•105 

•465 
•399 
•357 


0.96 

1-35 
2.73 

2.82 
2.58 

3-25 
.81 

1. 19 

2.36 

2.20 
2.42 
4.17 
2.60 
3-55 

3-iS 
2.35 
2.58 
5.00 

2.25 
1-55 
1.96 


5-2 

3-66 
3-54 

4.02 
4.68 

3-54 
•78 

.81 

2.97 

4.ir 
2.52 
303 
2.07 

3.51 

0.60 
0.93 
1.20 
1-05 

2.16 
2.19 
1-53 



cent below the phosphorus standard of 1.44 grams. These 
results indicate plainly that present food habits are more hkely 
to lead to a deficiency of phosphorus compounds than to a 
deficiency of protein in the diet, and it is not improbable that 
many cases of malnutrition are really due to an inadequate 
supply of phosphorus compounds. 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 257 

That the cases of low phosphorus dietaries are not to be 
ascribed simply to inadequacy of the total food supply of these 
families was shown by computing the amounts of phosphorus 
which would have been furnished in each case had the total 
amount of food been so increased or decreased as to furnish 
just 3000 Calories per man per day. On this basis only one 
of the 150 dietaries shows less than 0.96 gram, but 49 of them or 
2,1, per cent show less than 1.44 grams of phosphorus, as against 
only 2 per cent with less than 75 grams of protein, per 3000 
Calories. 

The table on the preceding page compares some staple foods 
as sources of phosphorus. 

It will be seen that, whether compared on the basis of weight, 
or of protein content or energy value, the different staple foods 
vary greatly in phosphorus content. In the planning of dietaries 
this fact should be kept in mind and care taken that foods 
fairly rich in phosphorus be adequately represented in each day's 
food. 

REFERENCES 

(See also the references at the end of the next chapter.) 
Abderhalden. Lehrbuch der Physiologische Chemie, 3 Aufl., Vorlesungen 

34-37- 
Anderson. The Organic Phosphoric Acid Compound of Wheat Bran, 

Journal of Biological Chemistry, Vol. 20, pages 463, 475, 483, 493 (1915). 
Babcock. Metabolic Water. Wisconsin Agricultural Experiment Station, 

Research Bulletin 22 (191 2). 
Bayliss. Principles of General Physiology, Chapters 7 and 8. 
Benedict. A Study of Prolonged Fasting. Carnegie Institution of 

Washington, Publication No. 203, pages 247-291. 
BoUTWELL. The Phytic Acid of the Wheat Kernel and Some of Its Salts. 

Journal of the American Chemical Society, Vol. 39, page 491 (191 7). 
BuNGE. Physiological and Pathological Chemistry, Chapters 7 and 8. 
Ehrstrom. Phosphorus Metabolism in Adult Man. Skandinavisches 

Archivfur Physiologie, Vol. 14, pages 82-1 11 (1903). 
Emmett and Grindley. a Study of the Phosphorus Content of Flesh. 

Journal of the American Chemical Society, Vol. 28, pages 25-63 (1906). 
S 



258 CHEMISTRY OF FOOD AND NUTRITION 

Eppler. Investigations of Phosphatids, especially those of the Egg Yolk. 
Zeitschrift fur physiologisclie Cliemie, Vol. 87, pages 233-254 (1913). 

FiNGERLlNG. Formation of Organic from Inorganic Phosphorus Compounds 
in the Animal Body. Zeitschrift fiir Biologic, Vol. 38, page 448 ; Vol. 
39, page 239 (191 2). 

Forbes. The Mineral Elements in Animal Nutrition. Ohio Agricultural 
Experiment Station, Bulletin 201 (1909). 

Forbes. Specific Effects of Rations upon the Development of Swine. 
Ohio Agricultural Experiment Station, Bulletins 213 and 283. 

Forbes and Keith. A Review of the Literature of Phosphorus Compounds 
in Animal Metabolism. Ohio Agriculture Experiment Station ; 
Technical Bulletin No. 5 (19 14). 

Hart, McCollum, and Humphrey. Rdle of the Ash Constituents of Wheat 
Bran in the Metabolism of Herbivora. American Journal of Physiol- 
ogy, Vol. 24, pages 86-103 (1910). 

Hawk. The Relation of Water to Certain Life Processes and more es- 
pecially to Nutrition. Biochemical Bulletin. Vol. 3, page 420 (1914). 

GuMPERT. Metabolism of Nitrogen, Phosphorus, Calcium, and Magnesium 
in Man. Medizinische Klinik, Vol. i, page 1037 (1905). 

Hart, McCollum, and Fuller. The R61e of Inorganic Phosphorus in 
the Nutrition of Animals. Wisconsin Agricultural Experiment Station, 
Research Bulletin No. i; American Journal of Physiology, Vol. 23, 
page 246 ( I 908-1909). 

Herbst. Calcium and Phosphorus in Growth at the End of Childhood. 
Zeitschrift der Kinderheilkunde, Vol. 7, page 161 (1913). 

Jordan, Hart, and Patten. ^Metabolism and Physiological Effects of 
Phosphorus Compounds of Wheat Bran. New York State .Agricultural 
Experiment Station, Technical Bulletin No. i ; and American Journal 
of Physiology, Vol. 16, page 268 (1906). 

McCollum. Nuclein Synthesis in the Animal Body. Wisconsin Agri- 
cultural Experiment Station, Research Bulletin No. 8 (1910). 

McCollum, Halpin, and Drescher. Synthesis of Lecithin in the Hen 
and the Character of the Lecithin Produced. Journal of Biological 
Chemistry, Vol. 13, page 219 (1912). 

McCri^dden and Fales. Complete Balance Studies of Nitrogen, Sulphur, 
Phosphorus, Calcium and Magnesium in Intestinal Infantilism. Jour- 
nal of Experimental Medicine, Vol. 15, page 450 (1912). 

McLean. On the Occurrence of a Mon-amino-diphosphatid Lecithin-like 
Body in Egg Yolk. Biochemical Journal, Vol. 4, page 168 (1909). 

Marshall. Comparison of Value of Organic and Inorganic Phosphorus. 
Journal of the American Medical Association, Vol. 64, page 573 (1915). 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 259 

Masslow. Significance of Phosphorus for the Growing Organism. Bio- 
chcmisches Zeitschrifl, Vol. 55, page 45 ; Vol. 56, page 174 (1913). 

Meischer. Biochemical Studies on the Rhine Salmon. Archiv fiir Ex- 
perimental Pathologic mid Pharmacologie, Vol. 37, page 100 (1896). 

Plimmer. The Metabolism of Organic Phosphorus Compounds. Their 
Hydrolysis by the Action of Enzymes. Biochemical Journal, Vol. 7, 
page 48 (1913)- 

Schlossmann. On the Kind and Amount of Phosphorus in Milk and its 
Significance in Infant Nutrition. Archiv fiir Kinderhcilkundc, Vol. 40, 
page I (1905)- 

Sherman, Mettler, ant) Sinclair. Calcium, Magnesium, and Phos- 
phorus in Food and Nutrition. U. S. Department of Agriculture, 
Office of Experiment Stations, Bulletin 227 (1910). 



CHAPTER X 

INORGANIC FOODSTUFFS AND THE MINERAL 
METABOLISM (Continued) 

Metabolism of Sodium, Potassium, Calcium, Magnesium 

The distribution of sodium and potassium in the body and 
some of their mutual relations in metabolism have been referred 
to in the section on the chlorides. The distribution and func- 
tions of calcium have been studied in greater detail than -those 
of magnesium. It is estimated that about 85 per cent of the 
mineral matter of bone, or at least three fourths of the entire 
ash of the body, consists of calcium phosphate. Probably over 
99 per cent of the calcium in the body belongs to the bones, the 
remainder occurring as an essential constituent of the soft tissues 
and body fluids. Of the magnesium in the body about 71 per 
cent is contained in the bones (Lusk). The muscles contain 
considerably more magnesium than calcium ; the blood contains 
more calcium than magnesium. 

That calcium salts are necessary to the coagulation of the 
blood has long been known and frequently cited as an example 
of the great importance of calcium salts to the animal economy. 
Equally striking is the function of these salts in regulating the 
action of heart muscle. 

It is well known that heart muscle may be kept beating nor- 
mally for hours after removal from the body when supplied, 
under proper conditions, with an artificial circulation of blood 
or lymph or a water solution of blood ash. Howell, Loeb, and 
others have studied the parts played by the several ash con- 

260 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 261 

stituents. The sodium salts take the chief part in the main- 
tenance of normal osmotic pressure and have also a specific 
influence. Contractility and irritabihty disappear if they are 
absent, but when present alone they produce relaxation of the 
muscle tissue. Calcium salts also, although occurring in blood 
in very much smaller quantity, are absolutely necessary to the 
normal action of the heart muscle ; while if present in quantities 
above normal, they cause a condition of tonic contraction (" cal- 
cium rigor "). There is a balance which must be maintained 
between calcium on the one hand and sodium (and potassium) 
on the other. Thus it is found that the alternate contractions 
and relaxations which constitute the normal beating of the heart 
are dependent in part upon the presence of a sufficient but not 
excessive concentration of calcium salts, and in part upon the 
quantitative relationship of calcium to sodium and potassium, 
in the fluid which bathes the heart muscle. Other active tissues 
of the body doubtless have analogous requirements as to in- 
organic salts. 

Regarding the adequacy of the ordinary intake to meet the 
specific requirements for sodium, potassium, calcium, and mag- 
nesium, it would seem that only in the case of calcium is it ordi- 
narily necessary to take thought in the selection of food materials 
or the arrangement of dietaries. The amount of sodium chlo- 
ride usually added to food is much more than sufficient to meet 
the sodium requirement of the body, even if the natural sodium 
content of the food be entirely disregarded. Potassium and 
magnesium are relatively abundant in meat (muscle) and also 
in most plant tissues, so that an ordinary mixed diet, unless it 
consist too largely of highly refined food materials, wall usually 
furnish a safe surplus of these elements. Dietaries entirely 
adequate in energy value and protein content may, however, 
contain too little calcium. Calcium requirement is therefore 
a question of much practical importance in human nutrition, 
and requires quantitative study. 



262 CHEMISTRY OF FOOD AND NUTRITION 

The Calcium Requirement 

Calcium constitutes a larger proportion of the body weight 
(about 2 per cent) than does any other of the " inorganic " ele- 
ments. It is very unevenly distributed in the body, over 99 per 
cent of the total amount being in the bones. It is also very 
irregularly distributed among the staple articles of food, many 
of which are extremely poor in calcium, while milk contains it 
in abundance. The " ordinary mixed diet " of Americans and 
Europeans, at least among dwellers in cities and towns, is prob- 
ably more often deficient in calcium than in any other chemi- 
cal element. 

In studying the effects of insufficient calcium, Voit kept a 
pigeon for a year on calcium-poor food without observing any 
effects attributable to the diet until the bird was killed and dis- 
sected, when it appeared that, although the bones concerned 
in locomotion were still sound, there was a marked wasting of 
calcium salts from other bones such as the skull and sternum, 
which in places were even perforated. Thus in adults there 
may be a continued loss of calcium without the appearance of 
any distinct symptoms because the losses from the blood and 
soft tissues may be replaced by calcium withdrawn from the 
bones. The injurious effect of an insufficient intake of calcium 
is of course more noticeable with growing than with full-grown 
animals. Abnormal weakness and flexibility of the bones (^re- 
sembling the condition of rickets in children) has been produced 
experimentally by feeding puppies with lean and fat meat only, 
while others of the same litter, receiving the same food, but with 
the addition of bones to gnaw, developed normally. In this con- 
nection it should be remembered that no animal is literally car- 
nivorous in nature, that is, none lives on flesh alone ; the animals 
called carnivora always eat more or less of the bones of their prey. 

According to Herter * many cases of arrested development in 

* On Injanlilism jrom Chronic Intestinal Injection, New York, 1908. 



INORGANIC FOODSTUFFS AND jNIINERAL METABOLISM 263 

infancy may be due to an insufficient assimilation of calcium 
from the food. Such a deficiency in the amount assimilated 
may be due to defective digestion or to a diet inadequate in 
calcium content. 

Many medical writers have attributed different diseases to 
inadequate calcium supply or disturbance of calcium metabo- 
lism. Conclusive proof or disproof of such theories would how- 
ever require more detailed and exact quantitative studies of 
the intake and output of calcium in health, and the amounts re- 
quired in normal nutrition at different ages and under different 
conditions, than have yet been made. 

The fact that normal urine has a low calcium content while 
the feces usually contain much the greater part of the calcium 
which has been taken in the food has often been interpreted as 
meaning that the absorption of food calcium is poor or that the 
calcium requirement of the body is low. It is now known, how- 
ever, from experimental evidence, that most of the calcium 
which has been absorbed and carried through the metabolic 
processes is normally excreted through the intestinal wall and 
thus leave? the body in the feces instead of the urine. When 
the diet is very poor in calcium and the output of this element 
materially exceeds the intake, the feces often contain a larger 
amount of calcium than was present in the food. 

Observations upon Breithaupt and Cetti showed a consider- 
able elimination of calcium in the feces during fasting. On the 
other hand, Benedict reports the result of a 31-day fast during 
which no feces were passed, but considerable quantities of 
calcium continued to be lost through the urine throughout the 
entire period. 

On account of the fluctuating distribution of the calcium be- 
tween urine and feces, conclusions regarding the calcium re- 
quirement can properly be drawn only from those experiments 
in which the amounts of this element in the food, in the feces, and 
in the urine have been directly determined. A compilation of 



264 CHEMISTRY OF FOOD AND NUTRITION 

such experiments has been made, and the reported results cal- 
culated to a uniform basis of 70 kilograms of body weight. On 
this basis, 63 experiments on 10 subjects (6 men and 4 women) 
show calcium outputs ranging from 0.27 to 0.78 gram and 
averaging 0.45 gram of calcium " per man per day." This 
includes the experiments which appear most rehable as indicat- 
ing the actual (minimum) requirement in that the food did not 
furnish an excess of calcium over the needs of the subject, and 
the calcium balance showed a reasonable approach toward 
equihbrium. It will be noted that this average of 0.45 gram 
calcium (equivalent to 0.63 gram CaO) represents the expendi- 
ture under conditions of closely restricted calcium intake. It 
corresponds to the average of 49.2 grams of protein per man per 
day reached on page 220, and approximates the minimum of 
actual need rather than a normal allowance. The margin for 
safety should probably be larger for calcium than for protein 
because of the likehhood of relatively greater losses in cooking 
and in digestion, while there is much less danger of any injurious 
result from surplus calcium than from surplus protein. Nelson 
and Williams have recently found the calcium output of four 
healthy men on normal unrestricted diet to range from 0.68 to 
1.02 grams of calcium (0.95 to 1.43 grams of CaO) per day. 
Here as in the case of protein the rate of metabolism to be ex- 
pected in a normal man on unrestricted diet and well fed, ac- 
cording to American standards, runs from 50 to 100 per cent 
above the amount which would probably suffice to meet the 
actual requirement. 

The calcium requirements of women are greatly increased 
by maternity. The need of an abundance of calcium for the 
rapidly growing skeleton of an infant is obvious. Before birth, 
and normally for several months after, this demand of the child 
is satisfied through the mother, whose calcium requirement is 
thus greatly increased. The weakening of the bones and teeth 
which is said to be a common accompaniment of pregnancy and 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 265 

lactation is held by Bunge to be largely due to a withdrawal of 
calcium from these structures to meet the mitritive require- 
ments of the embryo or the nursling. 

Lusk also emphasizes the importance of a diet rich in calcium 
for pregnant women, especially during the last ten weeks of 
pregnancy, when the fetus is storing calcium at a rapid rate. 
He cites * the data of Hoffstrom,t who computed in consider- 
able detail the demands of the fetus upon the mother for nitro- 
gen, phosphorus, calcium, and magnesium at different stages 
of intrauterine hfe. 

Strong confirmation of this has recently been obtained from 
investigation of farm animals. The experiments of Steenbock 
and Hart show that the production of milk in cows and goats 
causes a heavy drain upon the calcium of the skeleton unless 
the amount of calcium contained in the food be very abundant. 
They also point out that the mammary glands likewise make 
large demands upon the phosphorus supply and suggest that 
if the food be not rich in phosphorus the destruction of bone 
tissue to furnish phosphorus for milk production may result 
in still further loss of calcium from the body. 

Forbes and Beegle in studying the mineral metabolism of 
the milch cow found a heavy loss of body calcium, notwithstand- 
ing the fact that the food was beheved to supply liberal amounts 
of all essential elements and was eaten in sufficient quantity to 
induce storage of nitrogen. That calcium may be lost from the 
body while nitrogen is being stored has also been emphasized by 
several other investigators (Steenbock and Hart, Weiser, and 
others) . According to Forbes it may be necessary to continue high 
calcium feeding for some time after the cessation of lactation, in 
order to replace the calcium which the maternal organism has lost. 

In children after weaning and throughout early childhood there 
are apt to be frequent disturbances of the absorption and metab- 

* Lusk. Science of Nutrition, 3d edition, pages 380-390. 

t HoSstrom. Skandinavisches Archiv Jiir Physiologic, Vol. 23, page 326 (1910). 



266 CHEMISTRY OF FOOD AND NUTRITION 

olism of calcium, in some cases due to distinct disorders of 
digestion, in other cases to more obscure irregularities in nutri- 
tion. In order that these fluctuations shall not interfere with 
the steady growth of the child, it is obvious that the food must 
furnish a fairly Hberal surplus of calcium. Even under the 
most favorable conditions, a rapidly growing child will pre- 
sumably need more bone-making material in proportion to its 
total food than do adults, who alone have served as subjects for 
the metabolism experiments upon which our present estimate 
of calcium requirement is based. Camerer, in summarizing 
a long series of investigations upon the food requirements of 
children at different ages, concluded that the amount of calcium 
received by the average nursling is just about sufficient to main- 
tain a normal rate of growth, leaving little if any " margin of 
safety " ; and Bunge, from a comparison of the calcium contents 
of different staple foods, points out that calcium more than any 
other inorganic element is likely to be deficient as the result of 
the change of diet from mother's milk to other forms of food. 

Herter * estimates that in order to support normal growth 
of the skeleton there must be an average storage of about 37 
grams of calcium (51.6 grams of calcium oxide) annually through- 
out the period from the third to the sixteenth year. This means 
an average daily storage of somewhat more than o.io gram of 
calcium during this thirteen-year period. In order to accom- 
plish such a storage it is plain that the daily food of the child 
must contain a surplus of more than o.io gram of calcium per 
day beyond the amount required for maintenance, which latter 
amount should provide for the frequent failures of complete 
utilization which have already been mentioned. 

Herbst f studied the calcium metabolism of 6 boys between 
the ages of 6 and 14 years and found that they were storing from 
o.oio to 0.016 gram of calcium per kilogram per day, or 0.21 

* Infantilism. 

t Jahrh. Kinderheilkunde, Vol. 76. Ergdnzungshcjt, pages 40-130. 



INORGANIC FOODSTUFFS AND MINER.\L METABOLISM 267 

to 0.39 gram per capita per day. If normal growth of boys of 
these ages involves such a large storage of calcium, it is plain 
that the food of such boys must be rich in calcium if they are 
to develop advantageously. These boys consumed about 3 to 4 
times as much calcium in proportion to their weight as is required 
for the maintenance of men. 

From such considerations as these it is evident that one should 
be very liberal in calculating the amount of calcium to be sup- 
pHed to growing children. 

If 0.45 gram is the minimum on which an average man can 
maintain equihbrium, it would seem that the food of a family 
should furnish at least 0.67 gram* of calcium or 0.9 to i.ogram 
of calcium oxide per man per day. This is less than is advo- 
cated by such recent writers as Albu and Neuberg, Gautier, 
Obendoerffer, and Emmerich and Loew, or reported by Nelson 
and Williams ; yet about 50 per cent of the American dietaries 
which have so far been studied with respect to their ash con- 
stituents show less than 0.67 gram of calcium per man per day, 
and about 15 per cent of them show less than 0.45 gram calcium 
(0.63 granj CaO) per man per day. In some cases the deficiency 
in calcium is incidental to a general deficiency in the amount 
of food ; but if the food consumed in each dietary had been in- 
creased or decreased to just 3000 Calories there would have been 
less than 0.67 gram of calcium in 46 per cent, and less than 0.45 
gram in 8 per cent of the cases. Since inorganic forms of cal- 
cium are utilized in nutrition, the lime of the drinking water 
may be added to that of the food in calculating the amount 
consumed, and to this extent the actual nutritive supply may 
be greater than the dietary studies show, but unless a very 
" hard " water be used for drinking, it is unhkely that the Ume 
from this source will cover more than a small part of the cal- 
cium requirement. It is probable too that losses of food cal- 

* This amounts to setting a tentative "standard " 50 per cent higher than the 
average minimum, as in the cases of protein and of phosphorus. 



268 CHEMISTRY OF FOOD AND NUTRITION 

cium in cooking may fully offset the calcium obtained from the 
drinking water. Apparently the American dietary is more 
often deficient in calcium than in any other element ; certainly 
more attention should be paid to the choice of such foods as will 
increase the calcium content of the dietary. The use of more 
milk and vegetables with less meat and sugar will accomplish 
this and usually improve the diet in other directions as well. 

Calcium Content of Typical Foods 

The table on the following page shows the comparative 
richness in calcium of a number of staple articles of food. 

It will be seen that there are enormous differences in the cal- 
cium content of different foods, whether expressed in percentage 
of the food material or in relation to its protein content or 
energy value. Meat is exceedingly poor in calcium and is 
therefore, notwithstanding its high protein content, a very one- 
sided and inadequate source of " building material." Milk is 
so rich in calcium that one need take only 400 Calories of milk 
to obtain the entire day's supply of this element, while to get 
the same amount of calcium from round steak and white bread 
it would be necessary to take 10,000 Calories. Polished rice 
and new process corn meal are even poorer in calcium than white 
flour. The difference in calcium content between the whole 
grains and the " fine " mill products, while not so great as in 
the case of iron or phosphorus, is still considerable. In general 
the milling removes more than half of the calcium. The fruits 
and vegetables in general are fairly rich in calcium, while some 
of the green vegetables are strikingly so ; but in most cases the 
intake of calcium depends mainly upon the extent to which 
milk (and its products other than butter) enters into the dietary. 
A quart of milk contains rather more calcium than a quart of 
clear saturated lime water. By far the most practical means 
of insuring an abundance of calcium in the dietary is to use milk 
freely as a food. 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 269 



Approximate Amounts of Calcium in Food Material 



Food 



Beef, all lean . . 

Eggs 

Egg yolk . . . 

Milk 

Cheese .... 
Wheat, entire grain 
White flour . . 

Rice, polished 

Oatmeal . . . 

Beans, dried . . 
Beets .... 
Cabbage . . . 
Carrots .... 
Potatoes . ' . . 
Turnips .... 

Apples .... 
Bananas . . . 
Oranges . . . 
Prunes, dried . . 

Almonds . . . 
Peanuts . . . 
Walnuts . . . 



Calcium 

Per 100 Grams 

Edible 

Substance 



grams 
0.007 

0.067 
0.137 

0.120 
0.931 
0.045 
0.020 

0.009 

o.o6g 

0.160 
0.029 
0.045 
0.056 
0.014 
0.064 

0.007 
0.009 
0.045 
0.054 

0.239 
0.071 
o.oSg 



Calcium 
Per too 
Grams 
Protein 



grams 
0.03 

0-5 
0.9 

3-7 
3-5 
0-33 
0.18 

0.06 

0.4 

0.7 
1.9 
2.8 

5-1 
0.6 

5-0 

1.9 

0.7 

5-7 
2.6 

1.2 

0.3 
o-S 



Calcium 
Per 3000 
Calories 



grams 
0.18 

1-35 
I.I 

5-2 
6.4 
0.40 

0.18 

0.04 

0-5 

1.4 
1.9 
4-3 
3-7 
0-5 
4.8 

0.36 
0.27 
2.6 
o-S 

I.I 

0.4 
0.4 



Relations of the Inorganic Elements to Each Other 

It is evident from what has already been seen that the custom 
which has been more or less prevalent of referring to the ash or 
mineral matter of a food as if it were a substance is wholly 



270 CHEMISTRY OF FOOD AND NUTRITION 

illogical and incorrect. Food ash is always a mixture of the com- 
pounds of several different elements, and each element has its 
own functions and significance in nutrition. Even elements 
so closely related chemically as are sodium and potassium, or 
calcium and magnesium, are not only not interchangeable, but 
are, in some of their functions, directly antagonistic in their 
action in the body. Bunge's experiment showing the effect 
of potassium upon sodium excretion has already been noted. 
Meltzer and his associates have shown that the injection of 
magnesium salts has a marked general inhibitory effect, and that 
this can be quickly overcome by the subsequent injection of 
calcium salt. Summarizing the results of extended series of in- 
vestigations by himself and others, Meltzer stated, in the Trans- 
actions of the Association 0} the American Physicians for igo8 : 

" Calcium is capable of correcting the disturbances of the 
inorganic equilibrium in the animal body, whatever the. direc- 
tions of the deviations from the normal may be. Any abnormal 
effect which sodium, potassium, or magnesium may produce, 
whether the abnormality be in the direction of increased irrita- 
bility or of decreased irritability, calcium is capable of reestab- 
lishing the normal equilibrium." 

More recently Hart and Steenbock have found that the ad- 
dition of magnesium salts to an otherwise well-balanced ration 
tends to cause a loss of calcium from the body. Several other 
observers have reported similar unfavorable effects of magne- 
sium upon the metabohsm of calcium, and some are inclined 
to regard this as a matter of much importance to the well-being 
of the body. On the other hand, calcium seems to exert a favor- 
able influence upon the economy of iron in metabolism, inas- 
much as it appears to be possible to maintain equilibrium upon 
a smaller amount of iron when the food contains an abundance 
of calcium. 

It would thus appear that an adequate study of the subject 
should take account of the relative, as well as the absolute, 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 27 1 

amounts of the different inorganic elements of the food. Tables 
showing these elements for the different articles of food are in- 
cluded in the Appendix at the back of this book. Not only 
do the different food materials differ greatly in the absolute and 
relative abundance of the different elements, but the same is 
also true of the total food intake of different groups of people. 
Studies of 150 freely chosen American dietaries each covering 
the food of a group of people for a week or more show the follow- 
ing range and average intake, per man per day and per 3000 
Calories. 

Inorganic Elements in 150 American Dietaries 









Per Man Per Day 


Per 3000 Calories 




Min. 


Max. 


Average 


Min. 


Max. 


Average 


Calcium 
Magnesium 
Potassium 
Sodium 
Phosphorus . 
Chlorine . 
Sulphur . 
Iron . . 






0.24 
0.14 

1-43 
0.19 
0.60 
0.88 

0-51 
0.0080 


1.87 
0.67 

6.54 
4.61 
2.79 

5.83 
2.82 
0.0307 


0.73 
0-34 
3-39 
1.94 
1.58 
2.83 
1.28 
0.0173 


0.35 
0.17 

1.63 
0.22 
0.72 
0.83 
0.80 
0.0090 


1-47 
0-53 
5-27 
4-83 
2.30 
7.26- 

2.35 
0.0234 


0.73 
0.34 
340 
1-95 
1-59 
2.88 

1-30 
0.0174 



Since these dietary records did not show the quantities of salt 
used, the figures for sodium and chlorine in the table cover only 
the amounts in the food as purchased and are greatly below the 
actual intake of these elements. It will be seen that the intake 
of any given element may be widely different in the different 
dietaries, even though each represents the daily average for 
at least a week. To some extent this is due to the variable 
amounts of total food consumed, but even when the data are 
reduced to a uniform basis of 3000 Calories the differences be- 
tween minimum and maximum are still quite wide. 



272 



CHEMISTRY OF FOOD AND NUTRITION 



Output of Inorganic Elements during Fasting 

In view of the relationships discussed above it is of interest 
to examine the absolute and relative excretion of the different 
elements as recently reported by Benedict for a subject who 
fasted for thirty-one days. 



Urinary Excretion of Different Elements during a 31-DAY 
Fast (Benedict) 



Day 


Nitrogen 
gms. 


Chlo- 
rine 
gms. 


Phos- 
phorus 
gms. 


Sul- 
phur 
gms. 


Calcium 
gms. 


Magne- 
sium 
gms. 


Potas- 
sium 
gms. 


Sodium 
gms. 


1 


7.10 


3-77 


0.73 


0.46 


0.217 


0.046 


1.630 


2.070 


2 


8.40 


1.02 


1.08 


0.61 




•243 


.106 


1.368 


.926 


3 


11-34 


0.79 


1. 10 


0.68 




•243 


.106 


1.368 


.926 


4 


11.87 


0.59 


1.27 


0.67 




■243 


.106 


1.368 


.926 


5 


10.41 


0.41 


I-I5 


0.65 




.274 


.098 


1-445 


.276 


6 


10.18 


0.40 


1.02 


0.65 




.274 


.098 


1-445 


.276 


7 


9-79 


0.55 


0.80 


0.62 




•253 


.070 


.883 


•154 


8 


10.27 


0.32 


0.80 


0.64 


■ 


•253 


.070 


.883 


•154 


9 


10.74 


0.31 


0-93 


0.66 




•253 


.070 


.883 


■154 


10 


10.05 


0.28 


0.86 


0.61 




.220 


.072 


1.006 


.100 


II 


10.25 


0.36 


0.85 


0.62 




.220 


.072 


1.006 


.100 


12 


10.13 


0.31 


0.74 


0.62 




216 


.065 


— 


— 


13 


10.35 


0.32 


0.85 


0.62 




.216 


.065 


— 


— 


14 


10.43 


0.26 


0.81 


0.60 




.236 


.071 


.814 


.109 


15 


8.46 


0.16 


0.64 


0.50 




.236 


.071 


.814 


.109 


16 


9.58 


0.14 


0.89 


0.59 




.214 


.078 


— 


— 


17 


8.81 


0.12 


0.87 


0.53 




.214 


.078 


— 


— 


18 


8.27 


0.15 


0.81 


0.54 




•251 


•059 


.676 


-051 


19 


8.37 


0.16 


0.77 


0.55 




•251 


•059 


.676 


•051 


20 


7.69 


0.15 


0.64 


0.51 




• 237 


■053 


.644 


.066 


21 


7-93 


0.18 


0.70 


0.51 




• 237 


•053 


.644 


.066 


22 


7-75 


0.21 


0.69 


0.50 




.179 


•050 


•643 


.083 


23 


7.31 


0.18 


0.71 


0.51 




.179 


.050 


-643 


.083 


24 


8.1S 


O.IO 


0.68 


0.49 




.167 


.056 


-787 


.065 


25 


7.81 


0.18 


0.67 


0.49 




.167 


.056 


-787 


.065 


26 


7.88 


0.16 


0.65 


0.54 




•I S3 


•051 


.656 


•055 


27 


8.07 


0.16 


0.62 


0.52 




•153 


•051 


.6s6 


-055 


28 


7.62 


0.14 


0.59 


0..53 




•131 


.047 


-585 


.036 


29 


7-54 


0.12 


0.64 


0.52 




•131 


■047 


-585 


.036 


.SO 


7.83 


0.14 


0.61 


0.52 




.138 


.052 


.606 


.053 


31 


6.94 


0.13 


0.58 


0.49 




.138 


.052 


.606 


•053 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 273 

It will be noted that the nitrogen output and the output of 
chlorine run entirely different courses, especially in the early 
days of the fast. Each of the other elements seems to run its 
own course except that the sulphur tends to remain relatively 
constant like the nitrogen (both being derived from protein 
metaboHsm), and the output of sodium tends to run parallel 
with that of chlorine, since these two elements are excreted 
mainly in combination with each other as common salt. 

The Maintenance of Neutrality in the Body 

One of the interesting relationships among the ash constit- 
uents of foods is that between the acid-forming and the base- 
forming elements, since this has a direct bearing upon the im- 
portant problem of the maintenance of neutrality in the body. 

Although the reaction of normal human blood is alkaline to 
litmus, the actual excess of hydroxyl over hydrogen ions is 
found by modern methods to be so slight that blood as well as 
protoplasm is commonly spoken of as neutral. Thus Henderson 
writes : " Neutrahty is a definite, fundamental, and important 
characteristic of the organism." 

The normal processes of metabolism, however, involve a contin- 
ual production of acid (chiefly carbonic, phosphoric, and sulphuric) 
which must be disposed of in order to maintain this neutrality. 

The factors generally recognized as concerned in the main- 
tenance of neutrality are: (i) carbonates, (2) phosphates, 
(3) ammonia, (4) proteins. 

As preliminary to even a brief mention of the function of these 
different mechanisms for maintaining neutrality, it may be well 
to recur for a moment to the fundamental conceptions which have 
recently been so well summarized by Henderson as follows : * 

" First, the product of the concentrations of hydrogen and hy- 
droxyl ions (at constant temperature) is approximately constant. 
(H+) • (0H-) = c 

* Science, Vol. 46, page 78 (July 27, 1917). 
T 



274 CHEMISTRY OF FOOD AND NUTRITION 

Therefore the concentrations of these two ions always vary 
inversely 

^ ^ (0H-) 

" Secondly, if for convenience, just as the histologist uses mi- 
crons instead of meters, we adopt as unit concentrations of 
hydrogen and hydroxyl ions a very small quantity, viz. the 
concentration of these ions in neutral solutions, the value of 
this constant becomes unity.* 

(H+) ■ (0H-) = I, 

It may be noted that, using this unit of concentration, an ordi- 
nary decinormal solution of hydrochloric acid has a concentra- 
tion of hydrogen ions of nearly 1,000,000; and a decinormal 
solution of sodium hydroxide, a corresponding concentration of 
hydroxyl ions. 

" Thirdly, upon this basis the definitions of neutrality, acid- 
ity, and alkahnity are as follows : 

For neutrality, 

(H-^) = I = (0H-) 



For acidity, 
For alkalinity, 



(H+) > I > (0H-) 



(H+) < I < (0H-) 

'' Finally, in any solution containing a weak acid and its salts 
with one or more bases, regardless of the other components of 
the solution, the concentration of hydrogen ions is appro.xi- 
mately proportional to the ratio of free acid to combined acid. 

* The more usual method of expressing hydrogen ion concentration has been 
referred to in an earlier chapter (page 77). 



INORGANIC FOODSTUFFS AND MINER.\L METABOLISM 275 

This relation, however, holds only when the ratio of acid to salt 
is neither very large nor very small. 

" It is therefore evident that in the solution of any weak acid, 
when the quantities of free and combined acid are equal, the 
value of (H"'') is yfe ; if the ratio of acid to salt be 10 : i, (H"*") is 
10 k, if the ratio be i : 10, (H"^) is o.i k." 

In the case of carbonic acid and of acid phosphates the value 
of k is near enough to unity so that solutions containing acid 
carbonate or a mixture of primary and secondary phosphates 
must always remain nearly neutral. 

Carbonic acid produced in metabolism is chiefly disposed 
of by elimination as carbon dioxide through the lungs. For 
description of the mechanism and regulation of carbon 
dioxide elimination the reader must be referred to discus- 
sions of the physiology of respiration. Its bearing upon 
the problem of neutrality is summarized by Henderson as 
follows : 

" This substance is the chief excretory product of the organism. 
As such it must be eliminated promptly and completely. More- 
over, in that it leaves the body not in aqueous solution and as 
an acid, but almost exclusively in the form of gaseous carbon 
dioxide, there is no possibility of any variation of the permanent 
effect produced upon the reaction of the body by the elimina- 
tion of a definite amount of it. In the final regulation by ex- 
cretion it is not, therefore, concerned. And yet it has, in the 
process of excretion, a very important role in regulating the 
reaction of the body. This depends upon the fact that carbonic 
acid is not only a waste product, but also a normal constituent 
of the blood, and, as such, a principal factor in the physico- 
chemical regulation. Thus, if the ratio of carbonic acid to 
bicarbonates in a normal individual were i : 15, a large produc- 
tion of acid might cause a destruction of a third part of all the 
bicarbonates, producing in its place an equivalent amount of 
free carbonic acid. This, if nothing else occurred, would reduce 



276 CHEMISTRY OF FOOD AND NUTRITION 

the relative amount of bicarbonates from 15 to 10, and simul- 
taneously increase the free carbonic acid from i to 6. The ratio 
would now be 6 : 10, and since the hydrogen ion concentration 
is proportional to this ratio, this ion would suffer a nearly ten- 
fold increase of concentration. But at this point, or, more 
strictly speaking, continuously during the process, the excretory 
function intervenes. There is a tendency for the respiratory 
process to hold the tension of carbon dioxide in the blood 
nearly constant. This is the reason why carbonic acid has some- 
times been thought the respiratory hormone. Assuming that 
the exact quantity of carbonic acid set free by the reaction of 
neutralization were thus eliminated, the ratio would be reduced 
to 1 : 10, and the hydrogen ion concentration would rise but one 
third above its original value. More recent investigations, 
however, have shown that a tendency to acidity is accomplished 
by a lowering of the tension of carbon dioxide. Let us suppose 
that in this case the tension was lowered one third. The free 
carbonic acid of the blood would then become 0.67 instead of 
I. GO, and the ratio of acid to salt 0.67: 10, which is exactly 
equal to i : 15, the original ratio. Accordingly, the hydrogen 
ion concentration would be restored exactly to its original value, 
and the regulation by excretion would be quite perfect. Now 
there is abundant evidence to show that something very much 
like this is always occurring in the body, and, on the whole, I 
believe that the most delicate of all means to regulate the reac- 
tion of the body is to be found in this variation of the tension 
of carbonic acid during its excretion. Such considerations have 
strengthened the hypothesis that the hydrogen ion is the true 
respiratory hormone." (Henderson, he. cit.) 

Phosphates are regularly present in blood and urine in no- 
table amounts. From what has already been seen regarding 
the reaction of the blood, it may be inferred that in it the primary 
and secondary phosphates are normally present in such pro- 
portions as to produce a practically neutral mixture. In urine, 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 277 

on the other hand, acid phosphate predominates, because the 
kidney usually removes from the blood a larger proportion of 
primary than of secondary phosphate. Thus by virtue of this 
ability of the kidney to secrete an acid urine from a neutral 
blood, the excess of phosphoric acid produced in metabolism 
is readily disposed of. The disposal of the sulphuric acid pro- 
duced in the metabolism of protein is a more complicated prob- 
lem. Sulphuric is so strong an acid that it would soon poison 
the body unless quickly neutraUzed. 

When a fairly strong acid such as the sulphuric acid produced 
in the metabolism of protein enters a neutral or slightly alkaline 
solution of phosphates and carbonates such as the blood, it 
reacts with secondary phosphate to form primary phosphate 
and with bicarbonate to form carbonic acid. Since secondary 
phosphate (K2HPO4 or Na2HP04) is but faintly basic, and pri- 
mary phosphate (KH2PO4 or NaH2P04) is but faintly acid, the 
ratio of these phosphates may be considerably changed (i.e. a 
considerable amount of strong acid may be received by the 
phosphate mixture) without appreciably diminishing the alka- 
linity of the solution. Thus the blood may neutralize a con- 
siderable amount of acid without appreciable change in its reac- 
tion, or as ordinarily expressed, without alteration of its own 
neutrality.* 

* This property is also referred to as the "buffer efifect" of phosphate solutions 
and is of course connected with the capacity for secondary ionization, readily re- 
versible according to the reaction of the medium : 



Acid 


, ^ U2VO,- 


- ^ HP04= 


Alkaline 






H3PO4 
or 


^^P04= 




HsPO. 


± H2PO4- 
HP04= 

P04^ 


- + H+ 
= -|-H+ 
+ H+ ■ 








For discussion of acid-base equilibria in phosph 
Henderson cited at the end of the chapter. 


late solutions 


see the 


works of 



278 CHEMISTRY OF FOOD AND NUTRITION 

Ammonia, which is continually being formed in the body by 
deaminization of amino acids in the course of protein metabo- 
lism, constitutes another means of neutralization of acid. It 
will be remembered that, according as more or less acid is fojmed 
in, or introduced into, the body, a larger or smaller proportion of 
the nitrogen eliminated appears in the urine as ammonium salts.* 

Proteins, such as those of blood serum, are amphoteric sub- 
stances and can unite with acid by virtue of their amino, and 
perhaps other basic, groups. The constant presence of pro- 
teins in all parts of the body constitutes, therefore, a further 
mechanism for the immediate fixation of any strong acid pro- 
duced. This, however, is only a temporary and partial solution 
of the problem, since the acid thus fixed would remain to be dis- 
posed of when the protein is hydrolyzed to amino acids. 

The relations of these different factors in the maintenance 
of neutrality under normal conditions are summarized by Hen- 
derson as follows : f 

" The hydrogen ion concentration of the body has been seen 
to depend on the ratio 

H2CO3 
NaHCOs 

Acid reacting with this system causes a diminution of the de- 
nominator and an increase in the numerator of the fraction, the 
value of the fraction increases, and with it the hydrogen ion 
concentration. Hereupon the lung reduces the value of the 
numerator by diminishing the concentration of carbon dioxide 
in blood and alveolar air, the value of the fraction is restored 

* Two facts should, however, be kept in mind as possibly limiting the utility of 
this means of disposing of acid. In the first place, ammonium salts are generally 
regarded as somewhat toxic, their accumulation in the body being normally pre- 
vented by conversion into urea. Secondly, there is no good reason to suppose that 
the deaminization processes which form ammonia will always go on in the same 
cells and at the same time with the o.xidation processes which produce sulphuric 
acid. 

t Loc. cit., page 81. , 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 279 

more or less exactly to its original value and with it the concen- 
tration of the hydrogen ion. But the denominator is still below 
normal. To offset this, there occurs, on the one hand, a pro- 
duction of ammonia which takes the place in the urine of alkaH 
existing as salt in the blood. This alkali recombines with car- 
bonic acid, forming bicarbonate, and thus increasing the de- 
nominator. On the other hand the kidney removes less alkali 
in combination with phosphates than exist in this state in the 
blood. This alkah, too, helps to regenerate sodium bicarbonate, 
and thus to increase the denominator. Both of these processes 
are so regulated that the denominator is restored to normal. 
The concentration of carbonic acid responds through the ac- 
tivity of the respiratory mechanism, and the organism returns 
to its normal state. 

" These processes, of course, go on simultaneously and not in 
succession. They are, moreover, far less simple than such an 
analysis admits, for on the one hand the interaction of phos- 
phates and proteins has not been fully described, and, on the 
other hand, many of these variations influence other conditions 
and processes in the organism." 

The normal fluctuations of fixed acid production in healthy 
man on ordinary mixed diet are apparently taken care of in 
part by neutrahzation with ammonia and in part by the forma- 
tion and excretion of acid phosphate. In an experiment upon 
man by Gettler and the writer it was found that, of the extra 
acid formed in metabolism as the result of replacing the potato 
of a mixed diet by rice, about t,^ per cent was accounted for 
by the increased ammonia and about 40 per cent by the in- 
creased acidity of the urine, leaving a remainder which may have 
been ehminated, in part at least, through the skin, since no 
attempt was made to measure the amount or acidity of the per- 
spiration, or may have been neutraUzed by sodium or potassium 
carbonate in the blood or other fixed alkali from the body. In 
this experiment the intake and output of phosphorus was ap- 



28o CHEMISTRY OF FOOD AND NUTRITION 

proximately the same on both diets. The increased acidity of 
the urine, therefore, impHed an increased ratio of primary to 
secondary phosphate in the urine but not necessarily any in- 
crease in the amount of fixed base leaving the body. In the 
neutralization of sulphuric acid by means of phosphate, each 
molecule of hydrogen sulphate (representing one atom of sul- 
phur oxidized in protein metabolism) changes two molecules 
of secondary into primary phosphate. In order that the orig- 
inal condition of equiUbrium may continue, the surplus acid 
phosphate thus formed must be excreted. Whether or not 
this results in an increased excretion of phosphates and there- 
fore of sodium or potassium (or only, as in the experiment just 
cited, an altered ratio of primary and secondary phosphates in 
the urine), apparently depends not only upon the balance of 
acid-forming and base-forming elements in the food, but also 
upon the quantities of fixed bases and of phosphates which are 
being metabolized and of ammonia available from the protein 
metabohsm. It would seem that in any case in which sulphuric 
acid produced in metabolism is neutralized by the sodium or 
potassium carbonate of the blood, the resulting sulphate must be 
eliminated with corresponding loss of sodium or potassium and 
decrease of the capacity of the blood for combining with carbon 
dioxide. This is an important feature of acidosis. It is diag- 
nosed by determining the carbon-dioxide-holding capacity of 
a sample of blood serum and the result is expressed as the 
" alkali reserve " or " reserve alkalinity " of the blood. 

Thus while the phosphates and carbonates of the blood and 
tissues serve for the immediate neutralization of acid without 
appreciable change in the normal reaction of the blood or tissue 
itself, yet when much strong acid such as the sulphuric acid 
from protein metabolism is neutralized in this way, there is apt 
to result an increased output of the base-forming elements, 
which if not made good by the intake must tend to diminish 
the " reserve alkaUnity " or " alkali reserve " of the body. 



INORGANIC FOODSTUFFS AND MINEIL\L METABOLISM 281 

That an excess of acid-forming elements in food, even if long 
continued, does not necessarily lead to any apparent injury is 
shown by experiments of McCollum, in which rats were main- 
tained throughout a large part of their adult lives and produced 
healthy young on a diet of egg-yolk, in which there is a great 
predominance of acid-forming over base-forming elements. Yet 
in man an increase in the ammonia content and acidity of 
the urine is usually regarded (if pronounced and persistent) 
as indicating an unfavorable tendency. In this connection 
the decreased uric acid solvent power of the more acid urine 
is to be considered, especially in view of the present belief that 
the human organism does not destroy uric acid but must trans- 
port and excrete all that is produced in the body. Hindhede * 
found that the eating of vegetables, particularly potatoes, in- 
creases the capacity of the urine for dissolving uric acid. Fur- 
thermore, Hasselbalch f showed that the carbon dioxide tension 
of the alveolar (expired) air, which is indicative of the carbon- 
dioxide-carrying capacity and therefore of the reserve alka- 
linity of the blood, is influenced in a similar way by the food. 
On a diet rich in meat he found a tension of 37.8 mm. ; on an 
ordinary mixed diet, 38.3 mm. ; on a vegetarian diet, 43.3 mm. 

In an extended series of experiments, Blatherwick J Hkewise 
finds that foods which have a preponderance of base-forming 
elements lead to the formation of a urine which is less acid, 
both as regards hydrogen ion concentration and titration 
acidity, and which has an increased capacity for dissolving uric 
acid, while the ammonia content of the urine is diminished and 
the carbon dioxide tension of the alveolar air, indicative of 
reserve alkalinity, is increased. Conversely, foods with a 
predominance of acid-forming elements increase the urinary 
acidity and urinary ammonia, decrease the uric acid solvent 

* Skandinavisches ArchivfUr Physiologic, Vol. 26, pages 87, 384 (1912). 

t Biochemisches Zeitschrift, Vol. 46, page 403 (191 2). 

} Archives of Internal Medicine, Vol. 14, pages 409-50 (1914). 



282 CHEMISTRY OF FOOD AND NUTRITION 

power, and show, through lowered carbon dioxide tension of 
the alveolar air, a tendency toward depletion of the reserve 
alkalinity of the blood. 

The benefit to health which so generally results from a free 
use of milk, vegetables, and fruits in the diet may be attributable 
in part to the fact that these foods yield alkahne residues when 
oxidized in the body ; but this point should not be too greatly 
emphasized, for there are several other respects in which the 
eating of liberal amounts of milk, vegetables, and fruits is 
certainly beneficial, notably in supplying calcium, iron, and 
vitamines, and in improving the intestinal conditions. 

REFERENCES 

(See also the references at the end of Chapter IX.) 

Aron. Calcium Requirement of Children (and the Relation of Calcium 
Metabolism to Rickets). Biochemisches Zeitschrift, Vol. 12, page 28 
(1908). 

Aron and Frese. Utilization of Different Forms of Food-Calcium in the 
Growing Organism. Biochemisches Zeitschrift, Vol. 9, page 185 (1908). 

Aron and Sebauer. Importance of Calcium for the Growing Organism. 
Biochemisches Zeitschrift, Vol. 8, page i (1908). 

Benedict. A Study of Prolonged Fasting. Carnegie Institution of Wash- 
ington, Publication No. 203, page 247 (191 5). 

Blather WICK. Foods in Relation to the Composition of the Urine. Ar- 
chives of Internal Medicine, Vol. 14, page 409 (1914). 

Blauberg. Mineral Metabolism of Infants. Zeitschrift fiir Biologic, Vol. 
40 (N. S. 22), pages i, 36 (igoo). 

Camerer and Soldner. Ash Constituents of the New Born Infant and of 
Human Milk. Zeitschrift fur Biologic, Vol. 44 (N. S. 26), page 61 (1903). 

DiBBELT. Significance of Calcium Salts during Pregnancy and Lactation 
and the Influence of a Loss of Calcium upon Mother and Offspring. 
Beitrdge pathologische Andtomie (Zeigler), Vol. 48, page 147 (1910). 

Evvard, Dox, and Guernsey. Effect of Calcium and Protein Fed Preg- 
nant Swine upon the Size, Vigor, Bone, Coat, and Condition of the 
Offspring. American Journal of Physiology, Vol. 34, page 312 (1914)- 

FiTZ, Alsberg, and Henderson. Concerning the E.xcretion of Phosphoric 
Acid during Experimental Acidosis in Rabbits. Anr.rican Journal of 
Physiology, Vol. 18, page 113 (1907). 



INORGANIC FOODSTUFFS AND MINERAL METABOLISM 283 

Forbes. The Balance between Inorganic Acids and Bases in Animal 

Nutrition. Ohio Agricultural Experiment Station, Bulletin 207 (1909). 
Forbes. The Mineral Nutrients in Practical Human Dietetics. Scientific 

Monthly, Vol. 2, page 282 (1916). 
Forbes and Beegle. The Mineral Metabolism of the Milch Cow. Ohio 

Agricultural E.xperiment Station, Bulletin 295. 
GiVENS AND Mendel. Studies in Calcium and Magnesium Metabolism. 

Journal of Biological Chemistry, Vol. 31, pages 421, 435, 441 (1917). 
Hart and Steenbock. The Effect of High Magnesium Intake on Calcium 

Retention by Swine. Journal of Biological Chemistry, Vol. 14, page 

75 (1913)- 
Henderson. The Fitness of the Environment. 
Henderson. Equilibrium in Solutions of Phosphates. American Journal 

of Physiology, Vol. 15, page 257 (1906). 
Henderson. A Critical Study of the Process of Acid Excretion. Journal 

of Biological Chemistry, Vol. 9, page 403 (191 1). 
Henderson. The Regulation of Neutrality in the Animal Body. Science, 

Vol. 37, page 389 (March 14, 1913). 
Henderson. The Excretion of Acid in Health and Disease. Harvey 

Society Lectures for 1914-1915. 
Henderson. Acidosis. Science, Vol. 46, page 73 (1917). 
Kastle. On the Available Alkali in the Ash of Human and Cow's Milk 

and its Relation to Infant Nutrition. American Journal of Physiology, 

Vol. 23, page 284 (1908). 
LusK. Science of Nutrition, 3d edition, pages 215-222, 358-361. 
Mathews. Physiological Chemistry. 
McCoLLUM ANTJ HoAGLANTD. The Effect of Acid and Basic Salts and of 

Free Mineral Acids on the Endogenous Nitrogen Metabolism. Journal 

of Biological Chemistry, Vol. 16, page 299 (1913). 
MiCHAELis. Die Wasserstaffion-concentration. 
Nelson and Williams. The Urinary and Fecal Output of Calcium in 

Normal Men. Journal of Biological Chemistry, Vol. 28, page 231 

(1916). 
Osborne. Sulphur in Proteins. Journal of the American Chemical Society, 

Vol. 24, page 140 (1902). 
Robertson. On the Nature of the Chemical Mechanism which ISIaintains 

the Neutrality of the Tissues and Tissue Fluids. Journal of Biological 

Chemistry, Vol. 6, page 313 (1909). 
Sherman antd Gettler. The Balance of Acid-forming and Base-forming 

Elements in Foods and its Relation to Ammonia Metabolism. Journal 

of Biological Chemistry, Vol. 11, page 323 (1912), 



284 CHEMISTRY OF FOOD AND NUTRITION 

Steenbock, Nelson, axd Hart. Acidosis in Omnivora and Herbivora 

and its Relation to Protein Storage. Journal of Biological Chemistry, 
Vol. 19, page 399 (1914)- 

Steexbock axd Hart. Influence of Function on the Lime Requirement 
of Animals. Journal of Biological Chemistry, Vol. 14, page 59 (1913). 

Stoeltzner. The Two-fold Significance of Calcium in the Growth of Bone. 
Archiv fur die gesamlc Physiologic {Pjliigcr), Vol. 122, page 599 (1908). 

Taxgl. The Metabolism of an .\rtif1ciall3' Fed Child. Ibid., Vol. 104, 
page 453 (1904)- 

TiGERSTEDT. Ash Content of the Ordinary Dietary of Man. Skandina- 
visches Archiv fiir Physiologic, Vol. 24, page 97 (191 1). 

Ukderhill. Studies on the Metabolism of Ammonium Salts. Journal of 
Biological Chemistry, Vol. 15, pages 327, 337, 341 (1913). 

Van Slyke, Cullex, Stillmax, ant) Fitz. (.-Vcid Excretion and the .\lka- 
line Reserve.) Proceedings of the Society of Experimental Biology and 
Medicine, Vol. 12, pages 165, 184 (1915); Journal of Biological Chem- 
istry, Vol. 30, pages 289, 347, 369, 389, 401, 405 (1917)- 

VoiT (E.). Significance of Calcium in Animal Nutrition. Zeitschrifl fiir 
Biologic, Vol. 16, page 55 (1880). 



CHAPTER XI 
IRON IN FOOD AND ITS FUNCTIONS IN NUTRITION 

The amount of iron contained in the body is small, but its 
functions are of the highest importance. As previously noted, 
the iron content of the adult man or woman is estimated at 
only 0.004 per cent, or i part in 25,000 parts of the body weight, 
or rather less than 3 grams (hardly one tenth of an ounce) in 
the entire body. Much the greater part of this iron exists as a 
constituent of the hemoglobin of red blood corpuscles and is 
constantly functioning in the general metabolism as the carrier 
of the oxygen upon which all of the oxidative (energy-yielding) 
processes of nutrition depend. There is no considerable reserve 
store of relatively inactive iron in the body corresponding to 
the store of calcium and phosphorus in the bones. Hence if 
the intake of iron fails to equal the output there must soon result 
a diminution of hemoglobin, which if continued must mean a 
greater or less degree of anemia. The investigation of iron 
metabolism has therefore been largely connected with the 
study of anemia and of hemoglobin formation. 

Important changes of view in regard to the metabolism of 
iron have followed so closely and have depended so directly upon 
the progress of experimental methods that it seems desirable, 
in this case, to review in chronological order some of the more 
important steps in the development of our present knowledge. 

' Development of Modern Views 

It has long been known that iron is essential to the nutrition 
of both plants and animals, and that small amounts of the oxide 

28s 



286 CHEMISTRY OF FOOD AND NUTRITION 

or phosphate of iron occur in the ash of all natural food materials. 
A few decades ago it was assumed that the iron exists in the food 
as oxide or phosphate, and that hemoglobin is formed in the 
body by the combination of protein with inorganic iron. This 
view was hardly consistent with the ideas of animal metabolism 
taught by Liebig and generally held at the time, but appeared 
to be supported by the successful use of inorganic iron in the 
treatment of anemia. 

The results obtained in a number of investigations published 
between 1854 and 1884 threw doubt upon the utilization of in- 
organic iron for the production of hemoglobin, since they indi- 
cated that iron salts when injected act as poisons and are 
quickly eliminated from the blood, and when given by the 
mouth reappear almost quantitatively in the feces, little, if 
any, evidence of absorption being obtained except when the 
doses were so large or long continued as to cause irritation of 
the intestine. 

In the attempt to harmonize this result with clinical ex- 
perience it was suggested that the inorganic iron might act 
by absorbing the hydrogen sulphide of the intestine, thus 
protecting the food iron from waste. 

The view that medicinal iron acts by stimulation of the 
absorbing membrane was also advocated at about this 
time. It was held that the amount of iron in the ordinary 
food is always sufficient for the needs of the body, but that 
sometimes the intestinal mucous membrane becomes so blood- 
less that it cannot properly perform its functions of absorp- 
tion. Under such conditions inorganic iron was believed to 
stimulate and tone up the membrane so that in a short time 
the increased absorption of food iron makes good the defi- 
ciency in the blood. 

A very suggestive discussion of the metabolism of iron, 
the effects of a lack of iron in the food, and the amounts of 
iron required for the maintenance of the body in health was 



IRON IN FOOD AND ITS FUNCTIONS IN NUTRITION 287 

published by Von Hosslin in 1882, and long before this some 
attention had been given to the iron content of food materials 
by Boussingault. Boussingault's figures, however, are not 
sufficiently accurate to be of value at the present time, and 
httle attention was given to the subject discussed by Von 
Hosslin until it was reopened by Bunge about two years later. 

Bunge, in 1884, doubting the ability of the animal body to 
form hemoglobin from inorganic iron, undertook the study of 
the iron compounds of food materials in order to find in what 
form iron is normally absorbed and from what sort of iron com- 
pounds the growing organism ordinarily forms its hemoglobin. 
Practically all of the iron of eggs was found to be in the yolk. 
Yolk of egg does not contain any hemoglobin, but it must con- 
tain substances from which hemoglobin can be formed, since 
the incubation of the egg results in the development of hemo- 
globin without the introduction of anything from without. 
Bunge found no inorganic iron in egg yolk, but isolated con- 
siderable amounts of the precursor of hemoglobin, which he 
called " hematogen," and which exhibited the properties of a 
phosphoprotein containing about 0.3 per cent of iron in such 
firm " organic " combination that it gives none of the ordinary 
reactions of iron salts. In milk, cereals, and legumes similar 
organic compounds of iron and only traces of inorganic iron 
were found. At this time Bunge distinctly stated that iron 
occurs in food solely in the form of comphcated organic com- 
pounds which have been built up by the life processes of plants. 
In this form, said Bunge, is the iron absorbed and assimilated, 
and from these compounds hemoglobin is produced. 

In 1890 and subsequently, the absorption and assimi- 
lation of iron was studied by several experimenters, usually 
with particular reference to the question whether inorganic 
or synthetic organic compounds of iron are absorbed and 
assimilated, and especially whether such preparations contribute 
directly to the formation of hemoglobin. This question is, of 



288 CHEMISTRY OF FOOD AND NUTRITION 

course, extremely important, not only in connection with the 
therapeutic use of medicinal iron, but also in its bearing upon 
the iron requirements in health ; for if inorganic iron could be 
utilized in the body in exactly the same way as the complex 
organic iron compounds of the food, it would follow that the 
iron of drinking water could replace that of food, and the supply- 
ing of food iron would be a matter of indifference to a man whose 
drinking water suppHed a few milligrams of iron per day. In 
opposition to this view, Bunge held that little if any inorganic 
iron is assimilated, and that any effect of medicinal iron should 
be attributed to its action in protecting the food iron from loss 
in digestion, principally by absorbing the sulphur liberated as 
sulphide through intestinal putrefaction. 

Socin demonstrated the superiority of the iron of egg yolk 
over iron chloride by dividing a number of mice into groups, 
some of which were fed on a mixture of iron-free food and iron 
chloride, while others received the same iron-free food with the 
addition of egg yolk. None of the mice fed without organic 
iron lived for more than thirty-two days, while some of those 
receiving egg yolk lived as long as the experiments were con- 
tinued (sixty to ninety-nine days), and gained in weight. 

Gottlieb, recognizing the fact that iron might be absorbed 
and used by the body, yet finally excreted with the feces, 
determined the intestinal elimination of iron in dogs before 
and after subcutaneous and intravenous injections of known 
amounts of iron salts. From the results obtained it was esti- 
mated that practically all of the injected iron was eliminated 
by the intestines. 

Voit studied the metabolism of iron in dogs by direct ob- 
servations of absorption and elimination in isolated sections 
of the small intestine. Opening the peritoneal cavity, he 
separated the desired section, removed the contents, closed 
the ends, and left the sac thus formed in its normal position 
after having reunited the remainder of the intestine. Under 



IRON IN FOOD AND ITS FUNCTIONS IN NUTRITION 289 

these conditions the isolated section of intestine, while not 
coming in direct contact with anything taken by the mouth, 
would still receive its proportional share of anything elim- 
inated from the body through the intestinal wall. By kill- 
ing and examining animals which had been kept for some 
time after such an operation, Voit was able to compare the 
amount of iron eliminated through the intestinal wall with 
the amounts contained in food and feces, and thus to infer 
the extent to which the iron taken by the mouth was ab- 
sorbed and returned to the intestine for elimination. In 
fasting, the daily elimination found for each square meter 
of intestinal surface was 6 milligrams in the feces and the 
same amount (per square meter of surface) in the isolated 
loop of intestine. On food poor in iron the feces contained 
in each of two cases 10 milligrams, the isolated loops 6 and 
9 milligrams, of iron per square meter of intestinal surface; 
while on food rich in iron the corresponding figures for two 
experiments were 43 and 78 milligrams in the feces, and 8 
and 6 milligrams in the isolated portion of the intestine. 
Hence it appears that the iron eliminated in the feces during 
fasting or on food poor in iron came from the body through 
the intestinal wall, while most of the extra iron given with 
the food in the last two experiments passed through the al- 
imentary canal without being absorbed and metaboHzed. 

Stockman, in a paper upon the metabolism of iron, pub- 
Hshed in 1893, while discussing mainly the therapeutics of 
chlorosis (a type of anemia occurring in girls and young women) 
undertook to solve the question of the absorption of inorganic 
iron. He reasoned as follows : 

If inorganic iron preparations given hypodermically will 
cure chlorosis, there can in such cases be no possibiUty of the 
iron exerting its effect by the stimulation of the alimentary 
canal or by combining with hydrogen sulphide in the intestine. 

If iron sulphide given by the mouth cures chlorosis, it must 



290 CHEMISTRY OF FOOD AND NUTRITION 

be through absorption of the iron, since ferrous sulphide has 
no stimulating effect and cannot take up more sulphur. 

If bismuth, manganese, etc., take up hydrogen sulphide 
as readily as iron, but are inert in chlorosis, a further indirect 
evidence of absorption of iron is obtained. 

Stockman made experiments and observations upon hos- 
pital patients (of which he cites nine cases) which appeared 
to substantiate each of the three propositions, and thus to 
establish the fact that inorganic iron preparations cure chlorosis 
through being absorbed and utilized in the formation of hemo- 
globin. 

During the years 1 894-1 897 several investigators studied 
the absorption of different forms of iron by microchemical 
methods. Suitable stains having been found for the iden- 
tification of iron in the microscopic sections of tissue, it was 
possible by examination of the intestinal wall and the various 
organs and tissues of the body to follow the absorption, storage, 
and ehmination of the iron given medicinally or occurring in 
the food. Macallum investigated in this manner the behavior 
of inorganic salts of iron, iron albuminates, and the iron com- 
pound of the egg yolk, and found that iron taken in any of these 
forms may be absorbed from the small intestine. 

Woltering compared microchemically and by quantitative 
determination the amounts of iron in the livers of mice, rabbits, 
and dogs, fed with and without sulphate of iron, and reported 
an increase in the iron content of the liver and in the hemoglobin 
and red corpuscles of the blood as the result of feeding the iron salt. 

Gaule, using principally microchemical methods, found 
no reaction for iron in the chyle under normal conditions ; 
but a distinct reaction appeared in the lymph nodes, and 
extended to the spleen soon after the feeding of iron salt to 
rabbits. This absorption of inorganic iron was followed by 
an increase in the number of red corpuscles and percentage of 
hemoglobin in the blood. 



IRON IN FOOD AND ITS FUNCTIONS IN NUTRITION 29 1 

In the meantime, Kunkel and Egers studied especially 
the influence of iron salts upon the regeneration of blood 
after hemorrhage. Kunkel kept two dogs on a hmited milk 
diet, but gave one of them, in addition to the milk, iron in 
the form of albuminate. Each of the animals was bled 
every seven days, about one third of the total blood being 
taken each time. The iron in the drawn blood was deter- 
mined and ascertained to be greater than the amount sup- 
plied by the milk, but less than the total iron received by 
the dog which was fed with albuminate. The experiment 
was continued seven weeks, at the end of which time the 
blood and organs of the dog which had been kept on milk 
alone were poorer in iron than those of the dog which had 
received the iron albuminate. Only one animal was fed in 
each way, and no determinations of hemoglobin are recorded. 
According to Egers, the regeneration of blood after severe 
losses (one third of the estimated total) is very slow on food 
poor in iron, unless medicinal iron is also given, when the 
rate of regeneration becomes better, but not so good as on 
a diet supplying an abundance of food iron alone. Even 
when the diet was rich in food iron, however, Egers found 
that medicinal iron appeared to aid the regeneration of blood 
after hemorrhage. 

These investigations having shown that inorganic iron is at 
least to some extent absorbed and carried to organs which take 
part in the production of hemoglobin, it became of especial im- 
portance to determine by long-continued feeding experiments 
whether the inorganic iron thus absorbed can take the place of 
food iron in the production of hemoglobin under normal condi- 
tions. 

This question was studied by Hausermann in an extended 
series of experiments in Bunge's laboratory. The general 
plan of these experiments was to feed young animals from 
the end of the normal suckling period upon food poor in iron, 



292 CHEMISTRY OF FOOD AND NUTRITION 

usually milk and rice. One half of the animals, however, 
received ferric chloride in addition to this food. After the 
animals had been thus fed for from one to three months and 
had usually doubled in weight, they were killed, and the amount 
of hemoglobin in the entire body was estimated ; also, in 
the case of small animals, the total amount of iron. Ex- 
periments were carried out in this way upon 24 rats, 17 
rabbits, and 14 dogs. The results are summarized essentially 
as follows by Bunge : * 

The rats all became highly anemic, for at the end of the 
experiment the percentage of hemoglobin was diminished 
to about half that of animals from the same litter which had 
received their normal food, namely, meat, flies, yolk of egg, 
fruit, and vegetables. The rats which had taken ferric 
chloride in addition to the milk and rice contained no more 
hemoglobin than those which had received milk and rice 
only. Moreover, the amount of iron was in each case the 
same. In one experiment alone, in which the addition of 
ferric chloride was continued for three months, was the 
iron found to be double as much in the animals which had 
received it as in those which had only milk and rice. But 
here again the proportion of hemoglobin remained the same 
in both instances. We thus see that some iron is absorbed 
if small doses of iron are persisted in for a long time, as well 
as if large amounts be suddenly administered. But this 
inorganic iron, when absorbed, is not utilized in the for- 
mation of hemoglobin to any appreciable extent, but remains 
unused in the tissues. Whether inorganic iron was absorbed in 
the experiments which lasted only from one to two months can- 
not be decided ; it is possible that some of it was absorbed and 
was again eliminated in the same degree. Certainly no storing 
up nor increase of iron could be detected in the whole organism. 

* Physiological and Palholofiical Chemistry, Blakiston's edition. Philadelphia, 
1902, page 379. 



IRON IN FOOD AND ITS FUNCTIONS IN NUTRITION 293 

The experiments on rabbits gave less decisive results. The 
average proportion of hemoglobin in the animals that received 
inorganic iron was somewhat higher than that in the animals 
which were fed on milk and rice only. But when the great 
individual differences between various animals are taken into 
consideration, too much importance must not be ascribed to this 
slight divergence. At any rate, the amount of hemoglobin in 
the control animal, which received its normal diet — fresh 
green cabbage, bran, etc. — was nearly twice as high as in the 
animal which received the inorganic iron. 

The experiments upon dogs were not attended with decisive 
results, as dogs are not suitable animals for these experiments, 
owing to the variation in individuals. Moreover, the growth 
of these animals after the period of lactation is at a much slower 
rate, and their appetite is so enormous that they might readily 
be able to assimilate sufificient iron for hemoglobin formation 
even from a material so poor in iron as milk. In fact, Hauser- 
mann found the largest proportion of hemoglobin in a dog 
which had been fed exclusively upon milk. The animals which 
received ,ferric chloride in addition to a milk diet certainly con- 
tained no more hemoglobin than animals from the same litter 
which were fed on meat and bones. 

Abderhalden, following Hausermann, studied the subject 
even more exhaustively. In order to ascertain whether and 
to what extent sulphides normally exist in the alimentary 
canal, — a question of special importance in connection with 
one view of the mode of action of inorganic iron, — Abder- 
halden killed and examined rats, mice, cats, dogs, guinea 
pigs, and rabbits in the following way: Immediately upon 
kilHng the animal, the abdomen was opened and the intestinal 
tract from the esophagus to the rectum was ligated in sections. 
The contents of each section were then removed and tested 
qualitatively for sulphides. Hydrogen sulphide was obtained 
from the contents of the large intestine, but not from those 



294 CHEMISTRY OF FOOD AND NUTRITION 

of the small inlcstine nor of the stomach. Hence, if in- 
organic iron acts by improving the absorption of food iron, 
it must do so in some other way than by simply preventing 
its precipitation as sulphide, since this would not occur in the 
small intestine, where the principal absorption of iron takes 
place. The next step in the investigation was to study by 
microchemical methods the absorption of inorganic iron, its 
behavior in the body, and its elimination. Experiments 
were made upon 49 rats from 7 litters, 14 guinea pigs from 
6 litters, 12 rabbits from 2 Htters, 10 dogs from 3 Utters, and 
6 cats from 2 litters. 

From all of these experiments, Abderhalden concluded 
that the complicated iron compounds of the normal food, 
the iron in the form of hemoglobin, and hematin, and the 
inorganic iron, were all absorbed in the same general way, 
stored in the same organs, and eliminated by the same paths. 

In studying the utilization by the body of the different 
forms of iron, Abderhalden fed animals from the end of the 
suckling period, or, in the case of guinea pig, from birth, on 
food poor in iron, and divided each litter into two groups, 
one of which was given inorganic iron in addition. After a 
sufficient time the animals were killed, and the total hemo- 
globin in the body of each was estimated. Experiments of 
this kind were made upon 48 rats, 44 rabbits, 14 guinea pigs, 
17 cats, and 11 dogs. The animals fed with food poor in iron 
plus an addition of inorganic iron were unable to produce as 
much hemoglobin as those receiving normal food. 

In these experiments, Abderhalden had noticed some facts 
which indicated that the favorable influence of inorganic 
iron upon metabolism and blood formation was greater on 
a diet rich in food iron than when the amount of food iron 
was kept small. In order to test this, experiments were made 
with 66 rats, 10 rabbits, and 14 guinea pigs, in the manner 
already described, but with diets arranged to bring out this 



IRON IN FOOD AND ITS FUNCTIONS IN NUTRITION 295 

particular point. These experiments led to the conclusion that 
the greater the cjuantity of food iron present, the greater the 
influence of the inorganic iron upon the hemoglobin formation. 

Abderhalden's experiments also showed that the production 
of hemoglobin was not stimulated indefinitely by inorganic 
iron, but only for a short time, and he concluded that, while 
inorganic iron may be absorbed and may favorably influence 
blood formation, it is not used as material for the production of 
hemoglobin. It has also been found clinically that medicinal 
iron gives better results when used intermittently than when 
used continuously, which indicates that the action is due to 
stimulation rather than to the inorganic iron actually going to 
form hemoglobin. 

The results obtained by Tartakowsky * were more favorable 
to the view that hemoglobin may be formed from inorganic 
iron. He found that young growing animals fed on rice and 
milk gradually became anemic and finally ceased to grow ; but 
that when inorganic iron was added to the rice-milk diet the 
blood regained its normal iron content and the animal soon 
began to grow again. From such experiments together with a 
large number of microchemical observations, Tartakowsky 
concludes that medicinal (inorganic) iron is assimilated hke 
food iron and serves in the same way for the production of 
hemoglobin and the other organic iron compounds of the body. 
He further insists that Abderhalden's experiments should also 
be interpreted in the same way, since in many cases the animals 
which received inorganic iron in addition to their food formed 
more hemoglobin than the control animals. 

More recently, Schmidt f has described some interesting 
experiments upon mice with a similar iron-poor rice-and-milk 
diet. According to Schmidt this diet did not cause anemia 

* Archiv Jiir die gesamte Physiologic, Vol. 100, page 586; Vol. loi, page 423 
(1903, 1904). 

t Verhandlungen der Dcutsches Palhologisdies Gescllschafl,Vo\. 15, page gi (1912). 



296 CHEMISTRY OF FOOD AND NUTRITION 

in adult mice ; but the oflspring of mice which had been kept 
on such diet seemed to lack the normal reserve store of iron, and 
by continuing the milk-rice diet to the third generation there 
were obtained what this investigator describes as " iron-free 
families " of mice. In these the red blood cells were very poor 
in hemoglobin. From such a family of mice two sisters seven 
months old were selected ; one was continued on the milk-rice 
diet alone while the other was fed medicinal iron (Ferrum oxyda- 
tum saccharatum) in addition for eleven days ; then both were 
killed and examined. The first showed the typical anemic 
condition of these " iron-free families," the hemoglobin number 
and number of red blood cells being both less than half of the 
normal ; while in the second mouse, which had received medicinal 
iron for eleven days, the hemoglobin number and number of red 
blood cells were both about twice as high as in the first. This is 
held by Schmidt to show that medicinal iron does not merely 
stimulate the blood-forming organs to greater activity but does 
itself enter into hemoglobin formation. 

It is difficult to determine how much weight should be given 
to the findings of Tartakowsky and of Schmidt as opposed to 
the more extended and more quantitative experiments of Hauser- 
mann and of Abderhalden. 

While it cannot yet be stated positively that inorganic iron 
is or is not used by the animal body as material for the pro- 
duction of hemoglobin, the best medical opinion appears to 
support the conclusion reached by Abderhalden, that hemo- 
globin is derived essentially from the organic iron compounds 
of the food, while inorganic iron acts mainly if not entirely as 
a stimulus. This view is strongly supported by Von Noorden 
in his treatise on chlorosis in Nothnagel's Encyclopedia of 
Practical Medicine, and Ehrlich and Lazarus, writing on anemia 
in the same work, state : 

" It is not very probable that the (medicinal) iron stored by the 
liver and spleen is directly employed in the formation of hemo- 



IRON IN FOOD AND ITS FUNCTIONS IN NUTRITION 297 

globin ; on the contrary, the assumption first suggested by Von 
Noorden seems much more plausible, namely, that the iron exer- 
cises a direct irritative action on the function of the blood-making 
organs." 

The Iron Requirement of the Body * 

A very brief summary of the leading facts regarding the 
normal nutritive relations of iron may well precede the dis- 
cussion of the amount required. 

Iron is an essential element of hemoglobin and of the chro- 
matin substances, i.e. of the body constituents most directly 
concerned with the processes of oxidation, secretion, reproduc- 
tion, and development. The substances thus fundamentally 
connected with metabolism processes contain their iron in 
firm organic combination, as a constituent of their charac- 
teristic proteins; and the normal materials for the production 
of these body constituents are the similar iron-protein com- 
pounds of the food. 

The iron of the food is absorbed from the small intestine, 
enters the circulation by way of the lymph, and is deposited 
mainly in the liver, spleen, and bone marrow. Its final elim- 
ination takes place mainly through the walls of the intestines. 

Both inorganic and synthetically prepared organic forms 
of iron are absorbed from the same part of the digestive 
tract, stored in the same organs, and eliminated by the same 
paths as the iron of the food. These medicinal forms of iron 
often stimulate the production of hemoglobin and red blood 
corpuscles. 

Whether medicinal iron actually serves as material for the 
construction of hemoglobin is not positively known, but we 
have what appears to be good evidence that food iron is 
assimilated and used for growth and for the regeneration of 
hemoglobin to much better advantage than are inorganic or 
synthetic forms, and that when medicinal iron increases the 



298 CHEMISTRY OF FOOD AND NUTRITION 

production of hemoglobin, its effect is more beneficial in pro- 
portion as the food iron is more abundant — a strong indica- 
tion that the medicinal iron acts by stimulation rather than as 
material for the construction of hemoglobin. 

Evidently, then, we should look to the food rather than to 
medicines or mineral waters for the supply of iron needed in 
normal nutrition. 

Comparatively few experiments upon the amount of food 
iron required for the maintenance of equilibrium in man have 
been made. Cetti and Breithaupt eliminated 0.0073 ^^'^ 
0.0077 gram per day, respectively, when fasting. Three men 
observed by Stockman while receiving in the food about 
0.006 gram each per day eliminated 0.0063, o-oo9,3' ^^^d 0.0115 
gram, respectively. Von Wendt found his requirements to 
range in a number of experiments on different diets from 0.008 
to 0.016 gram per day, the largest amount being required in a 
case where the diet was deficient in calcium. In three experi- 
ments by Sherman in which the food contained 0.0057 to 0.0071 
gram of iron there was metabolized 0.0055, 0.0087, ^^^ 0.0126 
gram per day, respectively, and here also the amount of iron 
which sufficed for equilibrium when taken in the form of bread 
and milk (a diet rich in calcium) was insufficient when taken in 
the form of a diet (poor in calcium) consisting of bread and egg 
white, or bread alone. In this case, however, the difference 
in the economy of the metaboHsm of the iron may have been due 
not simply to the change in the calcium content of the food, but 
also to a superior nutritive value of the iron compounds of milk 
over those of bread and to the fact that the general conditions of 
digestion and nutrition were better when milk was included in 
the diet than when it was excluded. The nitrogen, phosphorus, 
calcium, and iron balances for two of these experiments per- 
formed upon the same man and with diets practically alike in 
energy value and protein content, are shown in the following 
table : 



IRON IN FOOD AND ITS FUNCTIONS IN NUTRITION 299 

Comparison of Balances of Different Elements 





Nature of 
Element 


Amount in Grams per Day 


Nature of Diet 


In food 


In feces 


In urine 


Balance 


Bread and milk . . 
Bread and egg white . 


Nitrogen 
Nitrogen 


10.10 
10.69 


0.46 
0.75 


13-09 
13.21 


- 3-45 

- 3-27 


Bread and milk . . 
Bread and egg white . 


Phosphorus 
Phosphorus 


1-55 
0.38 


0.57 
0.22 


1-03 

0.75 


— 0.05 

- 0-59 


Bread and milk . . 
Bread and egg white 


Calcium 
Calcium 


1.89 
o.io 


1-34 
0.34 


0.15 
0.07 


+ 0-A° 
- 0.31 


Bread and milk . . 
Bread and egg white . 


Iron 
Iron 


0.0057 
0.0065 


•0053 
.0085 


.0002 
.0002 


+ .OC02 
— .0022 



Here, although the nitrogen balance was practically alike 
on the two diets, there was on the bread and milk diet prac- 
tical equilibrium of phosphorus and iron and a storage of 
calcium, while on the diet of bread and egg white there were 
noteworthy losses of all three of these elements. 

Returning to the problem of the quantitative determination 
of the iron requirement it will be seen that in the cases in which 
the intake and output of iron have been determined, the require- 
ment appears to have varied with individuals and with the 
nature of the diet from 0.006 to 0.016 gram (6 to 16 milligrams) of 
iron per man per day. 

We might conclude from these results that a daily allow- 
ance of 10 to 12 milligrams of food iron should suffice for the 
maintenance of iron equilibrium in an average man under 
favorable conditions, but until the conditions which deter- 
mine a larger metabolism of iron are more clearly defined, it 
would seem desirable to set a higher standard, perhaps 15 
milligrams of food iron per man per day. 

In calculating the iron requirement for a family dietary, it 



300 CHEMISTRY OF FOOD AND NUTRITION 

is well to make the allowance for women and children more 
liberal than would be indicated by their total food require- 
ment. A woman requiring eight tenths as much food as a 
man will probably require more than eight tenths as much 
iron, and a child requiring half as much food may easily re- 
quire more than half as much iron; for the influence of 
menstruation, pregnancy, and lactation in women and of 
growth and development in children may reasonably be ex- 
pected to affect the demand for iron to an even greater extent 
than they affect the requirement for total food. It is probable 
that pregnancy and lactation increase the iron requirement 
of the mother by at least 3 milligrams per day, and at other 
times the losses of blood in menstruation must call for a greater 
intake of iron than would be needed by a healthy man of equal 
energy and protein requirement. 

Since milk is the sole food of young mammals during a 
considerable period of rapid growth, Bunge was surprised to 
find only small amounts of iron in milk ash. Comparing 
the composition of the ash of milk with that of the newborn 
animals of the same species, it was found that, while other 
constituents occurred in nearly the same relative proportions, 
the iron was six times as abundant in the ash of the young 
animal as in that of the milk on which it was nourished. That 
the suckling animal grows rapidly and increases its blood 
supply in spite of this apparent deficiency of iron in its food is 
due to the fact that the body contains a reserve supply of iron 
at birth. In confirmation of this statement Bunge and his pupils 
have published many analyses showing that the percentage of 
iron in the entire organism is highest at birth, and that during 
the suckling period the amount of iron in the body remains 
about constant, notwithstanding the increase in body weight. 

In all cases in which the young depend entirely upon the 
milk of the mother during the suckling period the body con- 
stituents of the young must evidently be derived entirely 



IRON IN FOOD AND ITS FUNCTIONS IN NUTRITION 301 

from the maternal organism either before birth through the 
placenta or after birth through the milk glands of the mother 
and the digestive tract of the young. Since disordered diges- 
tion may readily lead to defective absorption of the iron of 
the food, nature apparently takes the precaution of conveying 
the necessary iron from mother to offspring mainly by the 
safer method, i.e. through the placenta. Hence in the case of 
animals which feed solely upon milk for some time after birth, 
a relatively large amount of iron is stored before birth for use 
in the formation of hemoglobin during the suckling period. This 
has been shown by analysis to be true of children, puppies, 
kittens, and rabbits. On the other hand, guinea pigs, which feed 
on green leaves or other food rich in iron from the first day of 
life, are born without this reserve store of iron (Bunge). From 
recent analyses it appears that the percentage of iron in the 
human body is about three times as high at birth as at maturity. 
If it be assumed, as indicated by Bunge's work, that during the 
milk feeding of infancy the amount of iron in the body remains 
about constant, it would follow that the percentage of iron in the 
child's body would be reduced to that in the adult when the body 
weight becomes about three times what it was at birth — usu- 
ally when a little over one year old, — and that from this time 
on throughout the period of growth, care should be taken that 
the food is sufficiently rich in iron to provide not only for 
equihbrium, but also for the constantly increasing blood supply. 

Iron in Foods 

Little weight can be attached to such statements regarding 
the iron content of foods as are based upon the data obtain- 
able from the ordinary tables of ash analyses, since these have 
usually been obtained by methods which are Hkely to greatly 
overestimate the amount of iron. In the following table 
are shown the approximate amounts of iron now believed to 
be present in the average edible portion of typical food materials 



302 



CHEMISTRY OF FOOD AND NUTRITION 



expressed (i) in milligrams per loo grams of edible material, 
(2) in milligrams per 100 grams of protein, (3) in milligrams 
per 3000 Calories: 



Iron in Typical Food Materials 



Food 



Beef, all lean . . . 
Beefsteak, medium fat 

Eggs 

Egg yolk .... 
Milk, whole . . . 
Milk, skimmed . . 

Cheese 

Oatmeal .... 
Rice, polished . . 
White flour . . . 
Wheat, entire grain . 
Beans, dried . . . 
Beans, string, fresh . 

Beets 

Cabbage . . . . 

Carrots 

Corn, sweet . . . 
Peas, dried . . . 
Potatoes .... 

Spinach 

Turnips .... 

Apples 

Bananas .... 
Oranges .... 
Prunes, dried . . . 
Almonds .... 

Peanuts 

Walnuts .... 



Iron per ioo 
Grams Fresh Sub- 
stance, Milli- 
grams 



3.85 

2.2 

3-0 

8.6 

0.24 

0.25 

1-3 

3-8 

0.9 

i.o 

S-o 
7.0 
I.I 
0.6 
I.I 
0.6 
0.8 
5-7 
1-3 
3.6 
0-5 
0.3 
0.6 
0.2 
30 

3-9 
2.0 
2.1 



Iron per ioo 

Grams Protein, 

Milligrams 



16 
16 

22 

53 
7 
7 

5 



7 
37 
40 
48 
38 
69 

55 
26 

23 
55 

135 
39 
78 
47 
25 

143 
19 



Iron per 3000 
Calories, Milli- 
grams 



97 
47 
57 
69 
10 
20 

9 

26 

7 

7 

42 

60 

80 

39 

104 

40 

23 
46 
42 
450 
38 
15 
18 
12 

30 
18 



Percentages of iron in some other foods will be found in the 
tables of ash constituents in the Appendix. Using these recent 
data for iron in food materials, approximate estimates of the 



IRON IN FOOD AND ITS FUNCTIONS IN NUTRITION 303 

amounts of iron contained in 150 American dietaries have been 
made. The majority of these were found to furnish 14 to 20 
milligrams of iron per man per day. Apparently therefore 
the typical American dietary does not contain any such sur- 
plus of iron as would justify the practice of leaving the supply 
of this element entirely to chance. The available data rather 
indicate that foods should be selected with some reference to 
the kinds and amounts of iron compounds which they contain. 

Meats. — In meat as ordinarily eaten the iron exists largely 
as hemoglobin, due to the blood contained in the muscular 
tissue as usually sold and prepared for the table. Muscular 
tissue washed free from blood contains iron, but the amount 
is comparatively small. Since fatty tissue contains much less 
iron, the iron content of fat meat is much lower than that of 
lean, and in order to establish any useful estimate of the amount 
of iron in meat it is practically necessary to consider the lean 
tissue alone or to refer the iron to the protein content rather 
than to the gross weight of the meat. When expressed on the 
former basis, the results will still be influenced by the extent to 
which the' blood has been either accidentally or intentionally 
removed from the muscle. 

For fresh lean beef containing the full proportion of blood, 
the results obtained by most investigators are in satisfactory 
agreement, and the average figure, 0.00375 per cent iron in 
the fresh meat free from visible fat, can be accepted with 
Httle danger of serious error. This corresponds to about 15 
to 16 milligrams of iron per 100 grams of protein in beef, and 
since no certain differences in iron content in the flesh of dif- 
ferent species have been shown, it is assumed for the present 
that approximately the same ratio of iron to protein will hold 
for meats in general. 

The iron of meat, as already mentioned, is largely due to the 
blood retained in the muscular tissue. The nutritive value 
of blood is often questioned. So far as the iron compounds 



304 CHEMISTRY OF FOOD AND NUTRITION 

of the blood arc concerned, it seems to be established that 
hemoglobin and hematin may be absorbed and assimilated 
to some extent, but probably not to such good advantage 
as the iron compounds of eggs, milk, and vegetable foods. 

Eggs. — The edible portion of hens' eggs has shown as the 
average of several analyses 0.00303 per cent of iron. Whether 
the iron content of eggs can be increased by giving to poultry 
food rich in iron, is a disputed question. 

There can be no doubt regarding the assimilation and utiliza- 
tion of the iron compounds of eggs, since they serve for the 
production of all the iron-holding substances of the blood and 
tissues of the chick, there being no possibility of the introduction 
of iron from without during incubation. 

Milk. — Analyses of samples of cow's milk of various origin 
have given results varying from 0.0002 to 0.0003 per cent, and 
averaging 0.00024 per cent of iron in the fresh substance. 

It cannot be doubted that the iron of milk is readily absorbed 
and assimilated, since this constitutes the sole natural source of 
iron for all young mammals during a period of rapid growth. 
Moreover, metaboHsm experiments indicate that the iron of 
milk is likely to be utilized to especially good advantage, perhaps 
on account of its association with a high proportion of calcium. 

The question of the iron supply of infants fed upon diluted or 
modified cow's milk may, however, be considered at this point. 
It is now generally recognized that the best substitute for 
mother's milk is obtained by diluting whole cow's milk or top 
milk with a solution of lactose or maltose. By varying the 
richness of the milk or top milk used and the amounts of water 
and sugar added, the composition of the modified milk can be 
controlled at will. In order to ascertain whether the iron 
compounds of milk tend to condense upon the fat globules or 
for any other reason are altered in their distribution by the 
rising of the cream, a sample of milk was allowed to stand, and 
after the cream had risen, the iron and nitrogen contents were 



IRON IN FOOD AND ITS FUNCTIONS IN NUTRITION 305 

determined separately in the upper half, containing all of the 
cream, and in the lower half, which consisted of skimmed milk. 
These analyses showed in the upper half 0.000277 P^^ cent of 
iron and 0.54 per cent of nitrogen; in the lower half 0.000293 
per cent of iron and 0.59 per cent of nitrogen. It is evident, 
therefore, that the ratio of iron to nitrogen was practically the 
same in the cream as in the milk. It is therefore important to 
recognize that the iron content of cow's milk is little if any higher 
than that of human milk, while the protein content is at least 
twice as high ; that any modification of cow's milk which reduces 
its protein content will reduce the iron content in practically 
the same proportion, and that an infant fed upon cow's milk, 
modified or diluted to contain less than 3 per cent of protein, is 
probably receiving food poorer in iron than human milk. 
According to present estimates an infant fed on any modification 
of cow's milk must consume the equivalent of nearly a quart of 
undiluted milk or cream in order to obtain as much iron as is 
supplied daily in the milk of the average healthy nursing mother. 
Since no such quantity of cow's milk can safely be fed in early 
infancy, it is to be expected that during the first months of life 
the artificially fed infant will use up the surplus store of iron 
with which it was born more rapidly than will the child of the 
same age which receives the milk of a healthy mother. 

Grain products. — Iron in combination with protein matter 
is found in considerable quantity in the cereal grains, but the 
greater part of it is in the germ and outer layers, and so is 
rejected in the making of the " finer " mill products, such as 
patent flour, polished rice, and newrprocess corn meal. In 
view of the part which the iron of the germ takes in the sprouting 
of the seed and the nutrition of the young plant, there is little 
room for doubt that it is of value also in the animal economy. 
To test the value of the iron in the outer layers of the grain 
Bunge * carried out the following experiment : 

* Zeitschrift fur physiologische Chemie, Vol. 25, page 36 (1898). 
X 



3o6 



CHEMISTRY OF FOOD AND NUTRITION 



A litter of eight rats was divided into two groups of four 
each, one group fed upon bread from ftne flour, the other upon 
bread made from flour including the bran. At the end of the 
fifth, si.xth, eighth, and ninth weeks, respectively, one rat of 
each group was killed, and the gain in weight, the total amount 
of hemoglobin, and the percentage of hemoglobin in the entire 
body were determined. The average results were as follows : 



Effect of Feeding Different Kinds of Bre/Vd on Growth ant) Iron 
Content of Body in Experiments wtth R.ats 





Kind of Ration 


Gain in Weight 
OF Body 


Total 

Hemoglobin 

IN Body 


Proportion of 

Hemoglobin in 

Body 


White bread 

Bran bread 


Grams 

4.81 
20.76 


Grams 

0.2395 
0.3492 


Per cent 

0.613 
0.714 





Here the bran-fed rats not only made a much greater general 
growth, but developed both a greater amount and a higher 
percentage of hemoglobin. There can be no doubt that the 
iron and other ash constituents of the outer layers of the wheat 
were well utilized in these cases. 

Vegetables and fruits. — Not many direct studies upon the 
iron compounds of the fruits and vegetables have been made, 
but Stoklasa has separated from onions an iron-protein com- 
pound very similar to the hematogen obtained by Bunge from 
egg yolk, but containing a considerably higher proportion of 
iron. Preparations similar in properties were also obtained 
from peas and from mushrooms. 

In view of the fact that the herbivorous animals, which are 
less liable to anemia than the carnivora, obtain their normal 
food iron entirely from vegetable sources there is every reason 
to suppose that man makes good use of the iron of the fruits 
and vegetables in his diet. Moreover, since (as Herter has 



IRON IN FOOD AND ITS FUNCTIONS IN NUTRITION 307 

shown) anemic conditions and excessive intestinal putrefaction 
often go together, the bulkiness and laxative tendency of fruits 
and vegetables, along with their relatively high iron content, are 
advantageous in combating the conditions which give rise to 
excessive putrefaction, and at the same time increasing the 
supply of food iron. 

Among typical food materials omitted from the above 
table because of containing little if any iron, may be men- 
tioned fat pork, bacon, lard and suet, butter, salad oil, sugars, 
starches, and confectionery. All of these foods have high fuel 
value, and many are economical and highly important ele- 
ments in a normal dietary. Excessive use of these foods, 
however, would tend to satisfy the appetite and supply the 
body with the needed fuel without furnishing the desirable 
amount of iron. On the other hand, the fruits and fresh vege- 
tables are often regarded as of low nutritive value because of 
their high water content and low proportions of protein and fat. 
But it is largely this property which makes them especially 
important as sources of food iron, because they can be added 
to the diet without replacing the staple foods of high calorific 
and protein value, and without making the total food consump- 
tion excessive. Thus the above table shows plainly that the 
ratio of iron both to protein and to fuel value is high in nearly 
all of the typical fruits and vegetables, so that in most cases 
it would be necessary to increase only slightly the amount of 
protein and fuel value derived from these sources, in order 
to effect a material increase in the iron content of the dietary. 
The iron content of eggs is also high, but the cost of these 
is often such as to restrict their use in families of limited means, 
while present methods of drying and preserving tend to equalize 
the cost and increase the available variety of fruits and 
vegetables throughout the year. The ratio of iron to fuel 
value is also high in lean meat, but here, as has already been 
pointed out, the iron exists largely in the form of hemoglobin, 



3o8 CHEMISTRY OF FOOD AND NUTRITION 

which appears to be of distinctly lower nutritive value than the 
iron compounds of milk, eggs, and foods of vegetable origin. 
Especially in families where there are young children itlwould 
be a mistake to rely too largely upon meat as a source of iron. 
Von Noorden, who is one of the strongest advocates of a liberal 
use of meat in the adult dietary, says in regard to the feeding of 
children : 

" The necessity of a generous supply of vegetables and fruits 
must be particularly emphasized. They are of the greatest im- 
portance for the normal development of the body and of all its 
functions. As far as children are concerned, we believe we could 
do better by following the dietary of the most rigid vegetarians 
than by feeding the children as though they were carnivora, ac- 
cording to the bad custom which is still quite prevalent. . . . 
If we limit the most important sources of iron, — the vegetables 
and the fruits, — we cause a certain sluggishness of blood forma- 
tion and an entire lack of reserve iron, such as is normally found 
in the liver, spleen, and bone marrow of healthy, well-nourished 
individuals." 

In an experimental dietary study made in New York City 
it was found that a free use of vegetables, whole wheat bread, 
and the cheaper sorts of fruits, with milk but without meat, 
resulted in a gain of 30 per cent in the iron content of the diet, 
while the protein, fuel value, and cost remained practically the 
same as in the ordinary mixed diet obtained under the same 
market conditions. 

REFERENCES 

Abderhalden. Phj'siological Chemistry, English Edition, Chapter 17; 

Third German Edition, Chapter 35. 
BuNGE. Physiological and Pathological Chemistry, Chapter 25. 
Gaule. Resorption von Eisen und Synthese von Haemoglobin. Zeil- 

schrift fiir Biologie, Vol. 35, page 377 (1897). 
Gottlieb. Ueber die Ausscheidungsverhiiltnisse des Eisens. Zeilschrift 

fiir physiologische Chemie, Vol. 15, page 371 (1891). 



IRON L\ FOOD AND ITS FUNCTIONS IN NUTRITION 309 

Macallum. On the Absorption of Iron in the Animal Body. Journal 
of Physiology, Vol. 16, page 268 (1894) ; also Proceedings Royal Society 
(London), Vol. 50, page 277 (1891-1892); Quarterly Journal of Micro- 
scopical Science (London), Vol. 38, page 175 (1896). 

NoTHNAGEL. Encyclopedia of Practical IMedicine. Diseases of the Blood, 
pages 17, 339 (1905)- 

Sherman. Iron in Food and its Functions in Nutrition. Bull. 185, Office 
of Experiment Station, U. S. Dept. Agriculture (1907). 

SociN. In welcher Form wird das Eisen resorbirt ? Zeitschrift fiir physio- 
logische C hemic, Vol. 15, pages 93-139 (1891). 

Tartakowsky. Ueber de Resorption und Assimilation des Eisens. Pfi'i- 
gers Archiv ftir die gesammte Physiologic, Vol. 100, page 586; Vol. loi, 
page 423 (1903, 1904). 

Von Wexdt. Untersuchungen ueber den Eiweiss und Salz-Stoffwechsel 
beim JNIenschen. Skandinavisches Archiv fiir Physiologic, Vol. 17, pages 
211-289 (1905)- 

Woltering. Ueber die Resorbirbarkeit der Eisen-salze. Zeitschrift fiir 
physiologische Chemie, Vol. 21, page 186 (1895). 



CHAPTER XII 

ANTISCORBUTIC AND ANTINEURITIC PROPERTIES 

OF FOOD 

Recent investigations have shown that food furnishing suf- 
ficient amounts of proteins, fats, carbohydrates, and inorganic 
foodstuffs may not always prove permanently adequate. Some 
at least of the food materials which go to make up a completely 
adequate diet must have properties beyond those which have 
been considered in the preceding chapters. For the present 
these additional properties are best expressed in terms of their 
physiological effects. The term " deficiency diseases " has 
been introduced as a designation for those disorders which 
are thought to be due to dietary deficiencies of this sort, and 
the nature of the disorder arising from the use of any given diet 
serves to designate the property which has to do with the cause 
or prevention of the disease. Scurvy and beriberi have in recent 
years been considered the typical deficiency diseases. In nor- 
mal nutrition the occurrence of scurvy is prevented by the 
antiscorbutic properties of the food. Beriberi is primarily a 
disease of the nerves, a neuritis, and can be prevented by the 
use of food adequate in antineuritic substances or properties. 
Similarly some foods have growth-promoting properties beyond 
what can be accounted for by the proteins, fats, carbohydrates, 
and salts which they contain. 

As our knowledge in this field is not yet sufficiently developed 
to permit a satisfactory chemical classification of the subject 
matter, the antiscorbutic and antineuritic properties of foods 
will be considered in this chapter, and the growth-promoting 

310 



PROPERTIES OF FOOD 311 

properties in the next. The reader should keep clearly in mind 
the fact that these are matters of active investigation at the 
present time so that even while this is being printed, new re- 
sults tending to modify our views on these subjects may appear. 
The present text is written chiefly in the light of such investi- 
gations as were available in May, 1917- 

Scurvy and the Antiscorbutic Property of Food 

For centuries scurvy was one of the most common diseases 
in Europe and at times among people of European races in 
North America. It was most frequent and most severe in the 
more northern regions, where the people were often confined to 
a limited and monotonous diet of bread or other grain products 
and meat or fish through a large part of the year. As a rule 
fruits and vegetables were eaten only during their short natural 
season. 

On the long voyages which followed the discovery of America, 
sailors were often obliged to subsist for many months at a time 
on food even more restricted in variety than that of the winter 
diet of Europe because they were cut off not only from supplies 
of fresh fruits and vegetables but also from fresh meat. Their 
food supplies thus often consisted essentially of breadstuffs 
and salted meats. On such voyages there were many ex- 
ceedingly severe outbreaks of scurvy and it gradually came to 
be recognized that scurvy might be expected when men were 
kept for a long time on diets which lack fresh food. 

The European sailors whose experiences on their long voy- 
ages to America did so much to establish the relationship be- 
tween diet and scurvy and the fact that fresh foods, particularly 
fresh fruits and vegetables, have antiscorbutic properties, were 
also instrumental in bringing about a great diminution of the 
disease. They introduced into Europe from America the cul- 
tivation of the potato and since that time, as potato culture 
and the use of potatoes as food throughout the year have 



312 CHEMISTRY OF FOOD AND NUTRITION 

become more common in Europe, scurvy has become less 
common. 

For the past two or three generations serious epidemics of 
scurvy among adults have not often occurred except as the 
result of crop failure, imprisonment with inadequate food sup- 
ply, or siege. 

In all such cases of wliich we have accurate accounts the 
common feature appears to be the lack of potatoes or other 
fresh vegetable or fruit in the diet. Scurvy on shipboard is 
nov/ avoided by carrying more liberal quantities of potatoes 
among the rations, and, in case of long voyages, the juice of 
lemons or limes is taken specifically for its antiscorbutic prop- 
erties. 

Garrod called attention to the fact that foods shown by ex- 
perience to have good antiscorbutic properties (potatoes, lemon 
and lime juices, fruits and vegetables generally) are rich in 
potassium; and suggested that the cause of scurvy may be 
too small an intake of potassium — particularly of " acid veg- 
etable potassium " convertible into potassium carbonate on 
oxidation. 

However, the tendency of scurvy to occur epidemically (as 
well as some other pathological features) has also seemed sug- 
gestive of a bacterial origin and Litten after weighing the evi- 
dence available in the early years of this century wrote : * 
" However fascinating the potassium theory may be, it is by 
no means absolutely proven, and it does not contradict the 
view that scurvy may, in spite of this, be an infectious disease. 
Scurvy may perhaps be assumed to be an infectious disease of 
a non-contagious nature produced by a microdrganism which 
finds in a body deficient in potassium a favorable culture medium 
for its development." 

Wright, impressed with the fact that experience has shown 
scurvy to develop in cases in which the diet contains a pre- 

* Cabot's Diseases oj Metabolism (translation from Die Deutsche Kliiiik), p. 399- 



PROPERTIES OF FOOD 313 

ponderance of " acid forming " foods such as bread and meat, 
while foods of high antiscorbutic value, i.e. fruits and vegetables, 
are such as yield alkaline ash, was led to advocate the view 
(held also by Gautier) that the cause of scurvy is a sort of acidosis 
due to the constant production of a relative excess of acid in 
metabolism. An outbreak of the disease among the English 
soldiers besieged in Ladysmith during the Boer War gave Wright 
an opportunity to test his views and he found that in the scurvy 
patients the " titration alkalinity " (" alkali reserve ") of the 
blood was considerably below normal and that by feeding sodium 
or potassium salts of organic acids such as acetate, citrate, or 
lactate he was able to effect a rapid improvement both in the 
scurvy symptoms and in the blood alkalinity. 

Hoist and Frohlich, studying experimental scurvy in guinea 
pigs, find that some foods such as cabbage show a marked loss 
of antiscorbutic power as the result of simple heating or slow 
drying, while others (grains) develop antiscorbutic value in 
sprouting. In neither of these cases is the relation of acid-form- 
ing to base-forming elements altered and these authors there- 
fore consider that they have entirely disproven the acidosis 
theory of Wright and that antiscorbutic properties of foods 
have no connection with their ash constituents but are due to 
the presence of small quantities of a specific organic substance 
or substances, of undetermined chemical nature, and (in most 
cases at least) very readily destroyed by heat. 

Guinea pigs fed exclusively on bread or grain developed 
symptoms which Hoist and Frohlich considered to be " identical 
in all essentials with those of human scurvy." Since one of 
these symptoms is loss in weight and since animals may fail 
to eat enough of a one-sided diet to meet the energy require- 
ment, special experiments were made to establish the distinc- 
tion between the effects of scurvy and those of starvation or 
undernutrition. It was found that guinea pigs kept on an ex- 
clusive diet of fresh raw cabbage, dandelion greens, or even 



314 CHEIMISTRY OF FOOD AND NUTRITION 

carrots may die of starvation ; but they do not become scor- 
butic. Those kept on grain alone regularly became scorbutic. 
Those fed grain plus a moderate allowance of cabbage, dande- 
lion, carrot, potato, or other fresh vegetable remained normal. 
The antiscorbutic properties of other foods were then tested 
by adding them to a bread or grain diet and observing whether 
the guinea pigs developed symptoms of scurvy or not. 

Raw cabbage, dandelion greens, lettuce, endive, sorrel, 
potatoes, carrots, bananas, apples, and cloudberries all showed 
antiscorbutic properties — apparently in varying degrees. 
Apples and bananas were thought to be somewhat less effective 
than the potatoes, lettuce, greens, and berries. Cabbage and 
dandelion juices seem to lose their antiscorbutic properties more 
rapidly than the vegetables themselves. Fruit juices and sorrel 
juice on the other hand retain their efficacy as antiscorbutics 
remarkably well. Raspberry juice seemed but little injured 
by heating for i hour at ioo° or even iio°. Acidulated cab- 
bage or dandelion juice retained its antiscorbutic property 
much better than the natural juice of these vegetables. If, 
as these experiments indicate, the antiscorbutic property is 
due to the presence of some unstable substance, the latter would 
appear to be much more stable in an acid than in a neutral or 
alkaline medium. 

The effect of cooking was studied in the case of several dif- 
ferent foods with the following results : Cabbage cooked at 
ioo° for I to I hour was still a good antiscorbutic. Carrots 
cooked at ioo° for i hour showed a great diminution in antiscor- 
butic power. Cooking for ^ hour at the same temperature 
showed a less serious injury to the antiscorbutic property. 
Cauliflower was much injured by cooking for i hour at ioo°; 
when cooked only | hour it was a much better antiscorbutic. 
Dandelion leaves lost much of their antiscorbutic property when 
cooked for i hour at ioo°. Potatoes cooked at ioo° " in the 
usual way " (| hour) had excellent antiscorbutic properties. 



PROPERTIES OF FOOD 315 

Turnips and kohlrabi cooked at 100° had antiscorbutic power 
similar to cooked potatoes. Cloudberries retained their effi- 
ciency after cooking to a very marked degree. When cooked 
at 100° as usual they were still excellent antiscorbutics and 
were shown to retain this property when kept for at least 3 
months after cooking. From this it would appear that canned 
fruit which has been sterilized at temperature of boiling water 
and then kept in a cool place ought to be a good antiscorbutic 
even after many months, and in general that ordinary cooking 
of vegetables (or low temperature pasteurization of milk) de- 
stroys only a part of the antiscorbutic substance, and so the food 
still possesses antiscorbutic properties though not in as high 
degree as when raw. 

The results of several recent investigations are, however, 
not entirely consistent with the findings of Hoist and Frohlich. 

Funk, who had been a prominent advocate of the theory that 
scurvy is due to deficiency of a specific unidentified substance, 
has recently concluded that the disease produced in guinea pigs 
by a diet of oats (Hoist and Frohhch's experimental scurvy) 
may be due to acidosis. It has also been found independently 
by Jackson and by McCollum that guinea pigs are so suscep- 
tible to nutritive disorders with scurvy symptoms when placed 
upon experimental diets as to make the interpretation of such 
experiments exceedingly difficult. Jackson finds in the scor- 
butic tissues of the experimental animals bacteria of the Dip- 
lococcus type which appear to be specific to the scurvy lesions 
and pathogenic when inoculated into other guinea pigs. The 
results of such inoculation depend largely upon the diet ; guinea 
pigs fed on carrots, cabbage, and hay appear relatively im- 
mune, while those fed on grain or bread diet are much more 
susceptible. According to McCollum the physical character 
of the diet and of the resultant intestinal residues is responsible 
for guinea pig scurvy. His examinations of guinea pigs dying 
with scurvy symptoms reveal characteristically an abnormal 



3l6 CHEMISTRY OF FOOD AND NUTRITION 

accumulation of fecal material in the caecum. McCollum 
holds that the guinea pig will have scurvy on any diet which 
does not contain a succulent vegetable and that this is due to 
the anatomical character of the digestive tract, the caecum 
being relatively large and deHcate in this species and especially 
liable to the accumulation of fecal residues when the food is 
not of suitable physical character. His guinea pigs showing 
typical scurvy symptoms recovered after liberal doses of petro- 
leum oil. He therefore holds that guinea pig scurvy, although 
" referable to faulty diet, " is not a deficiency disease, the fault 
lying rather in the unsatisfactory physical character of the diet 
which leads to an injurious accumulation of material in the cae- 
cum. The immediate cause of the pathological symptoms of 
scurvy is not known. It may perhaps be due to absorption of 
toxic substances resulting from bacterial action in the caecum 
or to invasion of bacteria through an injured intestinal wall. 
In view of these results so recently reported by McCollum it 
becomes extremely difficult to interpret the work of Hoist and 
FrohHch, who apparently failed to reahze the part played by 
such digestive disorders. 

It also remains an open question whether guinea pig scur\y 
and human scurvy are referable to the same causes. 

Recently, as a result of war conditions, there has been re- 
newed interest in human scurvy and a tendency toward the 
view that this may be a disease in which two factors, a nutri- 
tional condition and an infection, may both be involved. 

It also seems probable that the terra " scurvy " may have 
been applied to more than one disease in man. 

Infantile Scurvy (Barlow's Disease) 

An investigation conducted by the American Pediatric 
Society in 1898 showed that infants developing scurvy had in 
nearly all cases been fed with heated milk or with proprietary 
foods. 



PROPERTIES OF FOOD 317 

Infantile scur\y is usually quickly cured by feeding either 
raw milk, or milk which has been pasteurized at a low tem- 
perature supplemented by some fresh fruit juice (usually orange 
juice). 

Investigations to determine whether children are subject to 
scurvy when fed exclusively upon pasteurized milk have given 
conflicting results, probably for two reasons: (i) pasteurization 
of the milk at difEerent temperatures or for different lengths of 
time in different cases, (2) differences in susceptibility to scurvy 
among infants.* Aging of the milk may also be a factor 
(Hess). 

Hess and Fish report that they have had a considerable 
number of cases of infantile scurvy among hospital children fed 
on milk pasteurized at 145° F. for 30 minutes or 165° F. for 
20 minutes. Orange juice was efficient as a preventive or 
cure and did not lose its antiscorbutic property when boiled 
for 10 minutes. It was found that the juice of the orange peel 
could be substituted for that of the orange as an antiscorbutic. 
Potato was found to be an excellent antiscorbutic for children, 
and the authors propose that potato water (made by mixing a 
tablespoonful of boiled potato in a pint of water) be used as a 
diluent instead of the barley water now commonly used in 
modifying cow's milk for infants. They held that if this is 
done, no other antiscorbutic will be necessary. 

In his later papers (1915, 1916), Hess reports that when 
milk which has been heated for 30 minutes at 145° F. is fed with 
sugar and cereal, but without orange juice or other antiscorbutic 
food, for from two to eight months there is usually a develop- 
ment of mild scorbutic symptoms, or a subacute scurvy such 

* Differences in susceptibility to scuny are to be expected in view of the well- 
known fact that when groups of men, as sailors and prisoners, are subjected to the 
same conditions and partake of the same rations, some become scorbutic while others 
do not. Physicians have also found that some infants show signs of scurvy when 
receiving an amount of antiscorbutic food which is amply sufficient for most infants 
and recover when a diet still richer in antiscorbutics is given. 



31 8 CHEMISTRY OF FOOD AND XUTRTTTON 

as might pass unrecognized. Such cases are apt to show some 
but not all of the classical symptoms of infantile scurvy and 
usually involve retardation of growth. Under these conditions 
the addition of an antiscorbutic food such as orange juice to 
the diet induces an increased rate of growth as well as rehef of 
such other scorbutic symptoms as may have developed. Even 
if, as some critics have suggested, the symptoms reported by 
Hess are somewhat different from those shown by well-de- 
veloped and clearly marked cases of infantile scurvy, the in- 
fluence which the presence or absence of antiscorbutic food in 
the diet was shown to exert upon the nutrition and rate of 
growth of the infant is a matter of considerable interest from 
the standpoint of food chemistry. 

More recently still (191 7), Hess finds that infantile scurvy 
is possibly not a single disease, and probably not a simple 
dietary disease. Use of pasteurized milk is a contributing 
cause, but the aging of such milk is quite as much a factor as 
the heating. The diet is held to be at fault in allowing the 
intestinal bacteria to elaborate toxins, while antiscorbutic 
foods improve intestinal conditions and are also beneficial as 
diuretics. 

Antineuritic Properties of Food 

Our knowledge of the antineuritic properties of foods has 
been obtained through the study of beriberi in man or of ex- 
perimental beriberi in fowls or pigeons. While the symptoms 
of beriberi are variable the disease is chiefly characterized by 
degeneration of the nerves beginning with those of the ex- 
tremities (" polyneuritis," " multiple peripheral neuritis "). 

For a long time beriberi was very common in the Orient 
(Malay States, Siam, parts of Japan and the Philippines) and 
in recent years beriberi has also been found in Newfoundland 
and Labrador. Cases are also occasionally reported from the 
southern and western parts of the United States. 



PROPERTIES OF FOOD 319 

Takaki, while Inspector General in the Japanese Navy, was 
much disturbed at the large proportion of men who suffered 
from beriberi, and in 1880 began a systematic investigation which 
indicated that the frequency of the disease was more closely con- 
nected with the nature of the food than with any other probable 
factor since climate was found to be without influence and the 
sanitary conditions on the Japanese ships were as good as those 
in the European navies which were not troubled with the disease. 

A Japanese naval vessel with 276 men on a g months' cruise 
from Japan to New Zealand, Valparaiso, and Honolulu had 169 
cases with 25 deaths. Another vessel with a similar crew was 
sent by Takaki over the same route with a ration in which 
the rice was decreased, the barley increased, and vegetables, 
meat, and condensed milk added. In this case only 14 men 
had beriberi and each of these had failed to eat his full allow- 
ance of the new foods. As the result of this experiment Takaki 
secured the adoption of his new ration for the entire Japanese 
navy with the result that the number of cases of beriberi soon 
became practically negligible. 

Takaki attributed this to the fact that the new diet was 
richer in protein, having a ratio of i part nitrogen to 16 parts 
carbon, whereas the old ration had only i part nitrogen to 28 parts 
carbon. The great reduction in beriberi was undoubtedly due 
to the change of diet, but not primarily to the increased protein 
intake. Apparently because the explanation available at the 
time was not sufficiently convincing, Takaki's great achievement 
was not fully appreciated, and medical opinion continued for 
several years to regard beriberi as possibly an infectious dis- 
ease. But no success attended the attempts to check the dis- 
ease by sanitation, while indications that the cause might be 
nutritional continued to be found. 

In 1907 Braddon published in his book, " The Cause and 
Prevention of Beriberi," a large amount of evidence connecting 
the disease with the eating of polished rice. 



320 CHEMISTRY OF FOOD AND NUTRITION 

At about the same time Fletcher, by experimenting with the 
diet in a lunatic asylum, showed that when 28 oz. of rice was 
fed daily with only small amounts of other food, the use of 
polished or unpolished rice was alone sufficient to determine 
the occurrence or non-occurrence of beriberi. 

During 1 907-1908 Fraser and Stanton took 300 laborers from 
Java into new and sanitary quarters in a virgin jungle and 
demonstrated in striking fashion that with rice as the main 
part of the diet, beriberi followed the use of polished but not of 
unpolished rice. Many other observations to the same effect 
were also published at about this time. 

In 1909, convinced that beriberi was related to diet, the 
U. S. Army Medical Commission in the Phihppines initiated 
changes in the rations of the " PhiHppine Scouts " and in 191 1 
Chamberlain was able to announce the eradication of the dis- 
ease from these troops by the substitution of unpolished rice 
(and a small quantity of beans) for the polished rice previously 
used. Until the year 1910, the number of hospital cases of 
beriberi ranged from 115 to 618 (the force numbering about 5000 
men). During 1910 changes in the dietary were begun and 
that year the cases dropped to 50. In 191 1 there were 3; in 
1912, 2; in 1913, none; in 1914 up to June 30 (date of latest 
available report) there was i. 

In 1908-1909, when beriberi was at its worst among the Scouts, 
the diet consisted essentially of 12 oz. of beef, 8 oz. of white 
flour, 8 oz. of potatoes, and 20 oz. of rice (ordinarily polished). 
The change in the ration, as finally decided upon after some 
months of experimentation, consisted in giving, in place of the 
20 oz. of polished rice, 16 oz. of unpolished rice and 1.6 oz. of 
dried beans. Experiments, made largely upon fowls as ex- 
plained below, have shown that while meat has some effect in 
preventing beriberi, an equal weight of beans, peas, or peanuts 
is much more efficacious. 

A further improvement could have been made by substituting 



PROPERTIES OF FOOD 32 1 

some whole grain product for the white flour since it is now 
known that a diet consisting too largely of white flour or bread 
may in itself be a cause of beriberi ; * but this appeared un- 
necessary inasmuch as the changes already noted sufficed to 
eradicate the disease. 

Chamberlain states, in fact, that the disease had disappeared 
as the result of adding the beans to the ration, before the sub- 
stitution of unpohshed for polished rice had been completed. 
He believes " that the consumption of beans to the daily amount 
of 1.6 ounces would, unaided, have prevented a recurrence of 
beriberi, but it would obviously be diflBicult to make sure that 
all the men ate their share of this article over long periods, and 
it is therefore much safer that the largest component of the 
diet, the rice, should be of the unpolished variety and by itself 
sufficient to prevent neuritis." 

Several other investigations gave similar results. These re- 
peated demonstrations of a close connection between a diet 
consisting too largely of polished rice and the occurrence of 
beriberi naturally gave a great impetus to experiments de- 
signed to find what constituents of the rice are directly con- 
cerned in the disease. 

Attempts to Isolate an Antineuritic Substance 

Such experiments were greatly facihtated by the fact, dis- 
covered by Eijkmann in 1897, that fowls develop a diseased 
condition closely resembhng beriberi in man, when they are 
fed exclusively upon polished rice for 3 or 4 weeks. Ohler 
(1914) finds that an exclusive diet of white bread, especially 
when made without yeast, has the same effect as the polished 
rice diet. This experimental beriberi of fowls (or " polyneuritis 
gallinarum ") does not occur when whole rice or even rice 
which has been partially milled so as to retain the inner bran 

* Little (1914). The prevalence of beriberi in Newfoundland and Labrador 
appears to be due to a diet too largely restricted to white bread. 
Y 



32 2 CHEMISTRY OF FOOD AND NUTRITION 

coat (pericarp or " silvcrskin ") is fed. It was soon found that 
rice polishings (bran) when added to the poUshed rice diet not 
only protected the fowls but also cured those which had already 
developed the disease. Aqueous and alcoholic extracts of the 
rice polishings also served to prevent or cure the disease. The 
same was found true of many ordinary foods such as meat, po- 
tatoes, beans, peas, and peanuts, the legumes being especially 
efficient. 

Aron working on Oriental beriberi in the Philippines, and 
Schaumann in Europe, centering his interest more particularly 
in ship beriberi, were both impressed with the fact that diets 
which cause beriberi are poor in phosphorus and that foods of 
good curative and preventive properties are rich in phosphorus. 
They were therefore inclined to regard beriberi as connected 
with a deficiency of phosphorus in the diet. Their attempts to 
prevent or cure the disease by adding definitely known phos- 
phorus compounds to the polished rice diet gave, however, for 
the most part negative results. In Aron's experiments the 
deleterious effects seemed to be reduced though not excluded 
when phyLin was fed. In Schaumann's experiments yeast 
lecithin and yeast nucleic acid seemed effective, but egg lecithin, . 
phytin, simple phosphates, and glycerophosphate showed no 
beneficial results. The direct evidence for the " phosphorus 
theory " is therefore weak and somewhat conflicting. (This 
does not exclude the possibility that deficiency of phosphatids 
may be at least a factor in the nerve degeneration as argued by 
Schaumann.) 

Furthermore, Fraser and Stanton showed that an extract of 
rice polishings which contained only 15 per cent of its total 
phosphorus was capable of preventing the neuritis, while the 
residue containing the other 85 per cent of the phosphorus was 
ineffective; and soon afterward Chamberlain and Vedder 
showed that an alcoholic extract of rice polishings which was 
highly protective contained only 0.0007 per cent of phosphorus 



PROPERTIES OF FOOD 323 

or less than one part in one thousand of the phosphorus originally 
present in the poUshings. 

Chamberlain and his associates also tried the effects of 
various inorganic salts, of sugar, phytin, lecithin, allantoin, 
choUne, and many of the amino acids, all of which proved in- 
sufficient to prevent the development of polyneuritis in fowls 
kept on a pohshed rice diet. On the other hand, they added to 
the knowledge of the properties of the antineuritic substance 
by a study of the effectiveness of rice bran extracts after dif- 
ferent treatment. The antineuritic substance was found to 
be insoluble in ether but soluble in alcohol or in water and 
dialyzable. It was not volatile but was destroyed by heating 
or by alkah ; in the presence of acid, it was more stable. It 
was not precipitated by lead acetate. They held the curative 
substance to be an organic base but not an alkaloid. Bean 
extracts were found to contain one or more substances having 
similar properties. Fresh milk, meat, and potatoes were also 
found to have antineuritic properties. 

Later in 191 1 and early in 191 2, several investigators inde- 
pendently and almost simultaneously succeeded in isolating 
what appeared to be specific antineuritic substances. 

Funk's experiments, begun about the middle of 1911, have 
attracted special attention since he was the first to announce 
(December, 191 1) the isolation of a definite chemical substance 
possessing the antineuritic property. Pigeons paralyzed by 
neuritis induced by a polished rice diet were able to run and 
fly within a few hours after administration of 2 to 8 milligrams 
of this substance, which appeared to be an organic nitrogenous 
base related to the pyrimidines and to which Funk gave the 
name vitamine. He described the preparation of such substances 
from rice bran and from yeast, and inferred the existence of 
the same or a similar vitamine in all foods which have anti- 
neuritic properties. Funk's view of the relation of vitamine to 
the phenomena of beriberi is as follows : The lack of vitamine 



324 CHEMISTRY OF FOOD AND NUTRITION 

in the food forces the animal to get this substance from its own 
tissues (with the result that there is wasting of the muscles 
causing emaciation unless accompanied by oedema). After the 
stock of vitamines available in the muscles begins to be scarce, 
there results a breaking down of the nerve tissue and the appear- 
ance of nervous symptoms such as are observed in beriberi. 

Funk called this beriberi vilamine. It constituted only 0.05 per cent of 
the rice polishings corresponding to about o.oi per cent in the whole grain. 

In March, 191 2, Edie, Moore, Simpson, and Webster (working independ- 
ently of Funk) described the isolation from yeast of a base which promptly 
cured pigeons suffering from polyneuritis. This base they described as 
having composition corresponding to the formula C7H17N2O6. They called 
it toniline. 

Schaumann (June, 191 2) reported the preparation of a phosphorus-free 
nitrogenous crystallizable base corresponding in general to the description 
given by Funk and exerting a marked restorative action upon polyneuritic 
pigeons. This base he considers the "activator" in the cure of polyneuritis, 
holding that it "mobilizes" the phosphatid substances which must be re- 
built into the degenerated nerve tissue in order to effect a permanent cure. 

In July, 191 2, Suzuki, Shimamura, and Odake, reported an extended 
investigation of experimental beriberi in which they had prepared from rice 
polishings by an independent method a base of high curati\e power which 
they called oryzanine. In preparing oryzanine they precipitated an alcoholic 
extract of rice polishings with tannin, decomposed the tannate by baryta, 
removed the barium by sulphuric acid, and precipitated the base as a picrate. 
Only 0.005 to 0.01 gram of oryzanine was required to make the dail}' diet 
of polished rice adequate for a pigeon. Since the pigeons ate 25 to 30 grams 
of rice per day this means that the oryzanine was only ^-^g^ to 55^5 ^^ the 
(dry) weight of the food eaten. Feeding 0.3 gram cured a dog that was 
already paralyzed by experimental beriberi.* 

It will be seen that these independent investigations all indi- 
cate that the antineuritic property shown by rice polishings, 
yeast, and other natural food materials is due to some basic 
nitrogenous substance or substances. Much work published 

* .\propos of the small quantities of vitamine or oryzanine necessary for pro- 
nounceci effects, Lusk calls attention to the fact that epinephrine (adrenaline), an 
essential of life, is present in the blood to the extent of only i part in 100,000,000. 



PROPERTIES OF FOOD 325 

sinfce 191 2 confirms this general view without estabHshing the 
chemical identity of either " Funk's base," or " toruline " or 
" oryzanine." Pending chemical identification of the naturally 
occurring antineuritic base or bases the term " vitamines " is 
commonly applied to them. 

While the antineuritic property of such " vitamine " has been 
demonstrated usually by experiments upon animals, WiUiams 
and Saleeby have used a vitamine preparation, made from rice 
polishings, in a case of human beriberi with good results. In 
connection with this work it was found that acid hydrolysis 
renders the antineuritic substance of rice polishings more active, 
or more rapid in its action. It is possible that in natural food 
materials or simple water extracts the vitamine may exist, 
either wholly or in part, in combination. This would account 
for the greater activity and also for the instability of the free 
" purified " vitamine as compared with the natural form. 

Seidell * has devised a method for obtaining a stable prepara- 
tion of the antineuritic vitamine by precipitating it with hy- 
drous aluminum silicate (Lloyd's reagent). 

While the general view has been that a given organism re- 
quires a given amount of vitamine to maintain health (pre- 
sumably a larger amount to effect recovery from disease in- 
duced by a previous deficiency), it was suggested by Braddon 
and Cooper (1914), and a few simultaneous experiments by Funk, 
that there is a connection between the metabolism of carbohy- 
drate and of vitamine, so that the amount of antineuritic sub- 
stance required by the organism increases with the quantity 
of carbohydrate metabolized. 

It has also been suggested that the neuritis of beriberi is 
due to a toxic effect, upon the nerves, of some substance formed 
in, or absorbed into, the system and that the vitamine, when 
present in normal amounts, acts as a protection or antidote 
against such toxicity. 

* Reprint No. 325 from the Public Health Reports, U. S. Public Health Service. 



326 CHEMISTRY OI- FOOD AND XUTRITION 

This hypothesis is difficult to lest and does not seem to have 
been much studied. Investigations designed to connect the 
physiological property with some definite chemical substance 
or type of molecular structure have, however, been continued 
and are yielding most interesting results. 

Relation of Chemical Structure to Antineuritic Action 

Williams has attacked this problem by synthesizing substances 
of known structure and testing them for curative action upon 
polyneuritic pigeons. Since such chemical examinations as 
had been made in connection with previous work upon active 
preparations from natural foods had suggested the presence of 
pyridine-Hke substances and also of hydroxyl groups in a 
benzene ring, Williams began by synthesizing a series of hy- 
droxy pyridines and other pyridine derivatives. Of these 
a-hydroxy pyridine, 2-, 4-, 6-trihydroxy and 2-, 3-, 4-trihydroxy 
pyridine were found to have curative power when tested upon 
polyneuritic pigeons. " The first of the curative substances 
tested was a-hydroxy pyridine. Three birds were treated with 
excellent results. However, three others later showed little or 
no improvement. On proceeding with the series of polyhydroxy 
compounds, a rapid striking cure was obtained with a preparation 
of 2-, 4-, 6-trihydroxy pyridine, followed by several partial or 
complete failures. A second and third fresh preparation, how- 
ever, produced two and three rapid cures respectively. . . . 
In each case all the cures obtained were of those pigeons which 
were first treated with a given preparation, while those treated 
with the same preparation a few days or weeks later invariably 
received no benefit. It was obvious that the substances had 
changed in some manner so as to lose the curative power. As 
there was no evidence of decomposition it seemed probable 
that it was due to isomerization." 

This suggested to Williams that an isomerism may be at least 
partially responsible for the instability of the natural " vita- 



PROPERTIES OF FOOD 327 

mines " of foods and in conjunction with Seidell he reinvesti- 
gated the antineuritic properties of yeast extracts from this 
standpoint and obtained results indicating that the antineuritic 
vitamine of yeast is an isomer of adenine. 

Voegtlin and White report that they were unable to confirm 
these observations on attempting to repeat the work of WilUams 
and Seidell. 

Continuing his work on the relation of chemical structure to 
antineuritic activity Williams finds that )8-hydroxy pyridine, 
nicotinic acid, trigonelline, and betaine are also capable of ex- 
istence in forms which are curative in the sense of being " able 
promptly to dissipate the acute symptoms of polyneuritis galli- 
narum." " On the basis of these results it may be concluded 
with reasonable certainty that the relief of the paralysis by such 
substances is intimately connected with a betaine-Uke ring." 

WiUiams calls attention * to the fact that, on theoretical 

H 

(CH)3 = N-CH2-CO C 

Betaine HCl iC 

HN-0 

Probable active form of a-hydroxy 
pyridine (Williams) 

grounds, the existence of betaine-like tautomeric modifications 
of the oxy- and amino-pyrimidines and purines is not less 
probable than in the case of the corresponding derivatives of 
pyridine, and proposes to search for active isomers in the pyri- 
midine series. 

REFERENCES 

Baumann and Hovard. Mineral Metabolism of Experimental Scur\'y 
of Guinea Pig. American Journal of the Medical Sciences, Vol. 153, 
page 650 (1917). 

Br addon. The Cause and Prevention of Beriberi. 

* Proceedings oj the Society Jar Experimental Biology andMedicinc, Vol 14, page 25. 



328 CHEMISTRY OF FOOD AND NUTRITION 

Braddon antj Cooper. The Influence of Metabolic Factors in Beriberi. 

Journal of Hygiene, Vol. 14, page 331 (1914). 
Chamberlain. The Eradication of Beriberi from the Philippine (Nativ-e) 

Scouts by means of a Simple Chanjic in their Dietary. Philippine 

Journal of Science, Vol. 63, pages 133-146 (191 1). Also Journal Ameri- 
can Medical Association, Vol. 64, page 1215 (1915). 
Chamberlain and Vedder. Etiology of Beriberi. Philippine Journal of 

Science, Vol. 6 B, pages 251-258, 395-404; Vol. 7 B, pages 39-52 

(1911-1912). 
Chick and Hume. Distribution Among Foodstuffs of the Substances 

Required for the Prevention of Beriberi and Scurvy. Journal of the 

Royal Army Medical Corps, Vol. 29, page 121 (1917). 
Darling. The Pathological Affinities of Beriberi and Scurvy. Journal 

of the American Medical Association, Vol. 63, pages 1290-1294 (1914). 
Edie, Evans, Moore, Simpson, and Webster. Anti-neuritic Bases of 

Vegetable Origin in Relation to Beriberi. Biochemical Journal, Vol. 

6, pages 234-242 (191 2). 
Emmett and McKim. The Value of the Yeast Mtamine Fraction as a 

Supplement to a Rice Diet. Journal of Biological Chemistry, \'ol. 32, 

page 409 (19 1 7). 
Frohlich. Experimental Investigation of Infantile Scur\-y. Zcilschrift 

fiir Hygiene und Infeclionskrankhcitcn, Vol. 72, pages 155-180 (191 2). 
Funk. Chemical Nature of the Substance which Cures Polyneuritis in 

Birds Induced by a Diet of Polished Rice. Journal of Physiology, \'ol. 

43, pages 395-400, and Vol. 45, page 75 (iQ", 1912). 
Funk. Die Vitamine und ihre Bedeutung fiir die Physiologic und Pathologic 

mit besonderer Beriicksichtigung der Avitaminoses (Beriberi, Skorbut, 

Pellagra, Rachitis) — Weisbaden, 19 14. 
Funk. Etiology of Deficiency Diseases (Beriberi, Scur\'y, etc.). Journal 

of State Medicine, Vol. 20, pages 341-368 (1913). 
Funk. Nature of the Disease due to an Exclusive Oat Diet in Guinea 

Pigs and Rabbits. Journal of Biological Chemistry, \o\. 25, page 409 

(July, 1916). 
Funk and Schonborn. Influence of Vitamine-free Diet upon Carbohy- 
drate Metabolism. Journal of Physiology, Vol. 48, pages328-33i (1914). 
FuRST. Experimental Scurvy. Zeilschrift fiir Hygiene und Infectionskrank- 

heiteti, Vol. 72, pages 1 21-154 (191 2). 
Harden and Zilva. The Alleged Antineuritic Properties of a-Hydroxy- 

pyridine and Adenine. Biochemical Journal, \'o\. 11, page 172 (1917). 
Hart and Lessing. Der Skorbut der Kleiner Kinder. 
Hart, Miller, ant) McCollum. Further Studies of the Nutritive De- 



PROPERTIES OF FOOD 329 

ficiencies of Wheat and Grain Mixtures and the Pathological Condi- 
tions Produced in Swine by their Use. Journal of Biological Chemistry, 
Vol. 25, page 239 (June, 1916). 

Hess anb Fish. Infantile Scurvy. American Journal of Diseases of Chil- 
dren, Vol. 8, pages 385-405 (1914). 

Hess. Infantile Scurvy. Journal of American Medical Association, Vol. 
65, page 1003 (1915). American Journal of Diseases of Children, 
November, 1917. 

HoLST AND Feohlich. Experimental Studies relating to Ship-Beriberi 
and Scurvy. Journal of Hygiene, Vol. 7, page 634 (1907). 

HoLST AND Frohlich. Experimental Scurvy. Zeitschrift fiir Hygiene 
und Infcctionskrankheitcn, Vol. 72, pages 1-120 (1912). 

HoLST AND Frohlich. Experimental Scurvy, II. Zeitschrift fur Hygiene 
und Infectionskrankheiten, Vol. 75, pages 334-344 (1913). 

Jackson et al. Experimental Scurvy in Guinea Pigs. Journal of Infec- 
tious Diseases, Vol. 19, pages 478-510, 511-514 (September, 1916). 

Little. Beriberi caused by Fine White Flour. Journal of the American 
Medical Association, Vol. 58, page 202g; Vol. 63, page 1287 (1912-1914). 

LusK. Science of Nutrition, 3d edition. Chapter 13. 

McCoLLUM. Supplementary Dietary Relationships among our Natural 
Foodstuffs. Harvey Society Lectures, 1916-1917, and Journal of the 
American Medical Association, Vol. 68, pages 1379-1386 (1917). 

McCoLLUM ANT) KENNEDY. The Dietary Factors operating in the Pro- 
duction of Polyneuritis. Journal of Biological Chemistry, Vol. 24, 
page 491 (1916). 

McCoLLLTM ANT) PiTZ. The Vitamiue Hypothesis and Deficiency Diseases. 
A Study of Experimental Scurvy. Journal of Biological Chemistry, 
Vol. 31, page 229 (191 7). 

Ohler. Experimental Pol3'neuritis. Effect of an Exclusive Diet of White 
Bread on Fowls. Journal of Medical Research, Vol. 31, pages 239-246 
(1914). 

Osborne and Mendel. The Role of Vitamines in the Diet. Journal of 
Biological Chemistry, Vol. 31, page 149 (1917). 

Schaumann. Preparation and Mode of Action of a Substance from Rice 
Bran which counteracts Experimental Neuritis. Archiv fiir Schijfs- 
mid Tropen-Hygiene, Vol. 16, pages 349-361, 825-837 (1912). 

Seidell. Vitamines and Nutritional Diseases. A Stable Form of Vitamine. 
Public Health Reports, Vol. 31, page 364 (February 18, 1916). 

Suzuki, Shimamura, ant) Odake. Oryzanine, a Component of Rice Bran 
and its Physiological Significance. Biochemische Zeitschrift, Vol. 43, 
pages 89-153 (1912). 



330 CHEMISTRY OF I'OOIJ AND NUTRITION 

Vedder. Beriberi. 

Vedder. The Relation of Diet to Beriberi and the Present Status of Our 
Knowledge of the Vitamines. Journal of the American Medical As- 
sociation, Vol. 67, page 1494 (November 18, 1916). 

VoEGTLiN. The Importance of Vitamines in Relation to Nutrition in Health 
and Disease. Journal of the Washington Academy of Sciences, Vol. 6, 
page 575 (1916). 

VoEGTLiN AND White. Can Adenine .Vcquire Antineuritic Properties? 
Journal of Pharmacology and Experimental Therapeutics, Vol. 9, page 
155 (December, 1916). 

Williams. The Chemical Nature of the "Vitamines." Journal of Biologi- 
cal Chemistry, Vol. 25, page 437 (July, 1916) ; Vol. 29, page 495 (1917). 

Williams. The Chemistry of the Vitamines. Philippine Journal of 
Science, Vol. 11 A, page 49 (191 6). 

Williams and S.\leeby. E.xperimental Treatment of Human Beriberi 
with Constituents of Rice Polishings. Philippine Journal of Science, 
Vol. 10 B, page 99 (1915). 

Williams and Seidell. The Chemical Nature of the "\'itamines," II. 
Isomerism in Natural Antineuritic Substances. Journal of Biological 
Chemistry, Vol. 26, page 431 (September, 1916). 

YoSHiKAWA, Yana, AND Menals. Studies of the Blood in Beriberi. Ar- 
chives of Internal Medicine, Vol. 20, page 103 (191 7). 



CHAPTER XIII 

FOOD IN RELATION TO GROWTH AND DEVELOP- 
MENT AND THE DIETARY DEFICIENCIES OF 
SOME INDIVIDUAL ARTICLES OF FOOD 

Nutritive Requirements of the Growing Organism 

" The upper limit of the size of an animal is determined by 
heredity. The stature to which an animal may actually attain, 
within this definitely fixed limit, is directly related to the way 
in which it is nourished during its growing period " (Waters). 

While feeding experiments upon growing animals and the 
influence of growth upon food requirements have been discussed 
to some extent in previous chapters, the great importance of 
adequate nutrition during the growing period demands special 
consideration. Recent investigations upon nutrition in growth 
are also of added interest in that the study of " growth-pro- 
moting properties " of food materials has broadened our con- 
ceptions of food values and of nutritive requirements in general. 

It is a familiar fact that the growing organism needs more 
energy, protein, and inorganic foodstuffs in proportion to weight 
than does one which is full-grown. But even a liberal diet 
made up of purified proteins, fats, carbohydrates, and salts 
does not suffice to support normal growth and complete de- 
velopment. 

Growth-Promoting Substances in Food 

Hopkins * found that the addition of very small amounts of 
milk to diets otherwise composed of purified foodstuffs sufficed 

* As early as igo6, Hopkins had found experimentally and published in brief 
{The Analyst, Vol. 31, page 395) the fact that an ani.Tial cannot live " upon a mixture 

331 



332 



CHEMISTRY OF FOOD AND NUTRITION 



to induce growth in young rals (Fig. 12), and Osborne and 
Mendel demonstrated that a similar growth-promoting effect 
was obtained when they introduced into their rations of isolated 

foodstuffs a moderate 
amount of " protein- 
free milk" — a powder 
made by removing the 
fat, the casein, and the 
albumin from cow's 
milk and evaporating 
the clear filtrate to 
dryness. Since in both 
these investigations it 
was found that milk 
ash does not show this 
property, it follows 
that milk must contain 
some water-soluble or- 
ganic substance which 
exerts a distinctly fa- 
vorable effect upon 
growth. A little later 
it was found both by 
McCollum and Davis 
and by Osborne and 
Mendel that the fat 
of milk (butter fat) 
also exerts a growth- 
promoting influence, which, as it is shared by only certain other 
fats, is probably not due to the glycerides themselves, but rather 

of pure protein, fat, and carbohydrate, and even when the necessarj' inorganic mate- 
rial is carefully supplied the animal still cannot flourish." Seeking further light 
upon the chemical nature of the essential substance contained in milk and some 
other natural foods but not in the purified foodstuffs, he deferred publication of the 
details of the experiments until igi2 {Journal oj Physiology, Vol. 44, page 425). 




-iU ifO 

Fig. 12. — Growth curves of rats. Lower curve 
six rats on artificial diet alone. Upper curve six 
similar rats receiving in addition 2 cc. of milk each 
per day. Abscissae time in days : ordinates aver- 
age weight in grams. Courtesy of Dr. F. Gowland 
Hopkins. 



FOOD IN RELATION TO GROWTH 333 

to a fat-soluble substance carried by butter-fat and the fat of egg 
yolk and in much smaller quantities if at all by most vegetable 
and meat fats. This fat-soluble substance (or something show- 
ing the same growth-promoting property) has also been found 
by McCollum to occur in certain plant tissues not rich in fat, 
notably in alfalfa and cabbage leaves and presumably in leaves 
generally. Normal growth and full development, as shown by 
ability to produce and nourish healthy young, demands, there- 
fore, in addition to adequate and appropriate supplies of proteins, 
fats, carbohydrates, and salts, at least two substances or kinds 
of substances which are distinguished by the solubility of one 
in water and of the other in fat. These substances, neither of 
which has yet been chemiically identified, are variously desig- 
nated by different writers. Hopkins used the term " accessory 
factors." Funk calls them "growth vitamines." McCollum 
criticizes the use of the term " vitamine " and proposes that until 
chemically identified the substances be known as " fat soluble 
A " and " water soluble B." The fats of milk, eggs, and cer- 
tain organs, and also the leaves of certain plants, are particu- 
larly rich in " fat soluble A " whereas many staple foods are 
very poor in this constituent. " Water soluble B " is more 
widely distributed, being found in the foods which have anti- 
neuritic properties, and it probably is the same as the sub- 
stance whose absence or insufficiency induces polyneuritis. 

Thus the feeding experiments with isolated foodstuffs have 
resulted in estabhshing the fact (until recently unsuspected and 
doubtless responsible for many of the failures met in earUer 
experiments) that there are required for normal nutrition, and 
most conspicuously during growth and development, these 
two factors A and B in addition to the previously known fac- 
tors of ample energy and adequate and appropriate supplies of 
protein and of inorganic foodstuffs. This has made it possible 
to proceed much more intelligently and effectively in the study 
of the relations of ordinary food materials to growth and de- 



334 CHEMISTRY OF FOOD AND NUTRITION 

velopment. In ihis conncctioh it is important, as McCnllum 
has emphasized, that growth and development be considered 
not only in terms of gain in weight at a normal rate, but also 
in reference to the capacity to produce and nourish healthy 
young at intervals normal for the species. A diet lacking in 
growth-promoting properties is apt to have an unfavorable 
effect upon reproduction and lactation. In some cases a de- 
ficiency may become manifest in connection with reproduction, 
even when it has not appreciably retarded growth. 

In a recent summary,* McCollum points out that the de- 
ficiency of wheat as a sole food has been found to be associated 
with the nature of its proteins, of its ash constituents, its lack 
of the " fat soluble A," and possibly a toxic factor. He states 
that when wheat and a good salt mixture are fed there is im- 
provement in the condition of the experimental animals for a 
Hmited time. A rat will grow for a month f on this com- 
bination and then stop, whereas he could not grow at all on 
wheat alone. On feeding wheat and casein only there is also 
a marked improvement for a time, and the same is true for a 
mixture of wheat and butter fat, " but in no case does the 
beneficial eflfect extend beyond the first month. These results 
we interpret to mean that there were two at least of the dietary 
factors involved, unless the trouble was all the result of toxicity 
in the wheat kernel. The next step was to feed wheat together 
with two purified additions as wheat, salts, and casein ; wheat, 
salts, and butter fat . . . combinations (which) will make a 
young rat grow to practically the normal adult size and at 
nearly the normal rate, but rats so fed will never produce 
young, and will never live much beyond a third of the usual 
length of life of a well-nourished animal. When we feed wheat 

* McCoUum. The Present Situation in Nutrition, Hoard's Dairyman, July- 
August, 1916. 

t In a month a rat makes as large a fraction of his total growth as is made by a 
child in from one to two years. 



FOOD IN RELATION TO GROWTH 335 

with all three of the purified additions, salts, protein, and but- 
ter fat, the animals are perfectly nourished and not only grow 
up at the regular rate but they are able to reproduce at fre- 
quent intervals and to successfully rear their young, and these 
young can complete the life cycle with no other food than that 
on which their parents Uved." 

Thus it now appears that the diet in order to be fully and 
permanently satisfactory must furnish (i) adequate energy 
value, (2) proteins sufficient in quantity and suitable in their 
amino acid make-up, (3) ash constituents each in sufficient 
quantity and all in well-balanced proportions, (4) " fat soluble 
A," and (5) " water soluble B." All of these factors are doubt- 
less necessary in order to make the diet really adequate at 
any time, but it is through studies of growth that the last-men- 
tioned factors were found, and all of the requirements are plainly 
more prominent in connection with growth, development, and 
reproduction than in the simple maintenance of healthy adults. 

Recognition of some of the factors just mentioned is too recent 
to have influenced the arrangement of many of the feeding 
experiments which have been made for the purpose of stud>ang 
the relation of diet to growth, so that it is not always possible 
to interpret the experimental data in terms of these five cate- 
gories. This can, however, be done to some extent. 

Influence of Restricted Food Supply 

(i) Energy 

When a diet of such character as would ordinarily meet all 
requirements is fed to a growing animal in amounts too small 
to meet the growth requirement, it is plain that such restriction 
may result in a deficiency of one, several, or all of the essential 
factors. If the diet is so selected as to be relatively rich in 
proteins, ash constituents, and the factors A and B, then re- 
striction of the amount of food will result primarily in an energy 



336 CHEMISTRY OF FOOD AND NUTRITION 

deficit. Waters has described experiments which appear to 
have been of this character. He reports numerous cases of 
young cattle kept on restricted amounts of food of suitable kinds, 
the restriction being such as to materially retard the increase 
in weight as compared with that of a full fed animal of the 
same age, or even to hold the young animal at stationary weight 
at an age when it should have been growing rapidly. In such 
cases of insufficiency of the total food (energy) intake the 
skeleton continues to grow, in height at least, while adipose 
tissue steadily disappears, and the muscles become more or less 
depleted. In a young animal subjected to this type of under- 
nourishment the skeleton grows in height to a much greater 
extent than in width. Thus in a full-fed steer the increase in 
length of foreleg and in width of chest were about equal, while 
in one whose rate of growth was retarded by sparse rations the 
width of chest increased only one third as much as the length 
of foreleg, and in another animal of the same age whose food 
was so restricted as to permit no increase in weight the increase 
of chest-width was only one eighth as much as the increase in 
foreleg. The ratios actually measured in typical cases were 
as follows: 





Condition of Animal 


Width . Length of 
OF Chest * Foreleg 


I — full fed 


I : 0.97 

I : 3-n 
I : 8.00 


II — • retarded 

Ill — maintenance * 





Along with the narrower skeleton the underfeeding resulted in 
muscles of smaller diameter, absence of subcutaneous fat, and 
a general emaciated appearance. Young animals thus held 
at constant weight when they should be growing are in reality 
undergoing starvation. To quote from Waters' paper: 

* Just enough food to maintain constant weight in an animal which should have 
been growing rapidly had he been more Uberally fed. 



FOOD IN RELATION TO GROWTH 337 

" Apparently the animal organism is capable of drawing upon 
its reserve for the purpose of sustaining the growth process for 
a considerable time and to a considerable extent. Our experi- 
ments indicate that after the reserve is drawn upon to a certain 
extent to support growth, the process ceases and there is no 
further increase in height or in length of bone. From this point 
on, the animal's chief business seems to be to sustain hfe. 
This law applies to animals on a stationary live weight as well 
as those being fed so that the live weight is steadily declining, 
and indeed to those whose ration, while above maintenance, 
and causing a gain in hve weight, is less than the normal growth 
rate of the individual. Such an animal will, while gaining in 
weight, get thinner, because it is drawing upon its reserve to 
supplement the ration in its effort to grow at a normal rate." 

" On all the animals under observation the retardation in 
height growth did not manifest itself at all until after the 
sparse nourishment had been continued for several months. 
On the other hand, the influence upon the width development 
was observable much earlier, and width development ceased 
altogether, in the case of animals on a maintenance or submain- 
tenance ration, long before the height development had ceased." 

" Our experiments have shown that within certain limits 
which are not yet at all well defined, retarded growth means 
retarded development of the organism. Thus an animal at 
twelve months of age and weighing on account of sparse nour- 
ishment only 400 pounds when it should under natural nourish- 
ment have weighed 800 pounds, has not its tissues as fully 
developed and matured as they would have been had the 
nourishment been normal. For example, we find that the flesh 
of steers 14-16 months old that had been sparsely fed through- 
out their lives presented the general characteristics such as 
color, flavor, etc. of veal or the flesh of calf. At this age the 
flesh of a highly nourished animal possessed the characteristic 
color, texture, and flavor of beef. Prof. Eckles has shown that 



538 CHEMISTRY OF FOOD AND NUTRITION 

dairy heifer calves heavily fed reach sexual maturity at from 
eight to ten months of age, whereas similarly bred individuals 
that were sparsely fed did not reach the stage of puberty under 
from 16 to 19 months of age." 

" An animal which has been retarded and which in its earlier 
hfe has shown an asymmetric development, may tend later to 
correct this asymmetry, and it is not inconceivable that this 
may be fully corrected before the animal has reached a state of 
complete maturity, or a point where growth ceases altogether." 

Somewhat similar experiments have been performed upon 
dogs by Aron. Here also when the food was suitable in char- 
acter but too Hmited in amount to support normal growth the 
young animals grew in length and height but became thinner. 
Because of the " growth impulse " such an underfed young 
animal burns his reserve of body material to cover the deficit 
in the energy intake " in his endeavor to grow at a normal 
rate." Such a condition continued indefinitely results after a 
time in cessation of all growth and finally in death from star- 
vation. A dog which by underfeeding had been kept for a 
year at the weight which he had when 5 weeks old and had be- 
come long, tall, and very thin, and was then fed liberally im- 
mediately gained in weight and circumference but appeared 
to have lost the capacity for further growth in length and 
height. If, however, the period of underfeeding be not too 
prolonged, the animal on subsequently receiving ample food 
may regain normal proportions and grow to full normal size. 

Since stationary weight in the young animal which is at- 
tempting to grow with an insufficient energy supply does not 
mean cessation of all growth but growth of bone and brain at 
expense of adipose tissue and to some extent also of muscle, 
it follows that the body of such an animal gradually changes in 
composition, the percentages of fat and perhaps protein becom- 
ing less while the percentages of water and ash increase. If, 
however, the diet is rich in fat, as in experiments upon mice 



FOOD IN RELATION TO GROWTH 339 

recently reported by Mendel and Judson, a simple diminution 
of the amount of food to a point where gain in weight ceases 
may not result in any such general replacement of fat by water, 
perhaps because in such a case the stunting may be due to in- 
sufficiency of some of the other factors rather than to an energy 
deficit. 

The experiments of Mendel and Judson also yield interesting 
data regarding the changes which normally occur in the water, 
fat (ether extract), and ash content of the body during its most 
active growth. From 88 analyses of the entire bodies of mice 
the following changes in composition were found : (a) increase 
in solids from 16 percent at birth to a maximum of 35 per cent 
at fifty days with a subsequent decrease to ^t, per cent ; (b) de- 
crease in the proportion of water in the fat-free substance from 
85.5 per cent at birth to 73 per cent in the adult mouse ; (c) rapid 
increase in fat from 1.85 percent at birth to about 10 percent 
followed by slow increase to 1 2 per cent ; (d) increase in ash 
content from 1.86 per cent at birth to 3 per cent in the adult 
mouse. 

(2) Protein 

As explained in earlier chapters (text and figures, pages 55-68 
and 224-226), it was shown by Osborne and Mendel that with 
a diet adequate in all other respects any one of a number of 
purified proteins such as casein, lactalbumin, or edestin might 
serve as the sole protein both for maintenance and for growth, 
while gliadin as sole protein food sufficed for maintenance but 
not for growth, and zein as sole protein did not suffice even for 
maintenance. Gliadin contains adequate tryptophane but only 
about I per cent of lysine ; addition of lysine to the gliadin 
ration made it adequate for growth. Zein contains neither 
tryptophane nor lysine ; addition of tryptophane to the zein 
diet makes it adequate for maintenance; addition of both 
tryptophane and lysine makes it adequate for growth. 



340 CHEMISTRY OF FOOD AND NUTRITION 

When " adequate " proteins were fed in progressively re- 
stricted amounts, i.e. in diminishing percentage of the food 
mixture, Osborne and Mendel found that with diflerent pro- 
teins different amino acids prove to be the limiting factors — 
e.g. lysine in the case of edestin, cystine in the case of casein. 
With 15 to 18 per cent of casein in the food mixture the rate of 
growth was normal; with 9 to 12 per cent of casein the rats 
grew more slowly but normal rate of growth was resumed upon 
adding 3 per cent of cystine to the food mixture. With only 
4.5-6 per cent of casein the addition of the 3 per cent cystine 
did not make the growth normal, indicating that with casein 
reduced to this point the supply of some other amino acid had 
become insufficient.* 

Another case in which cystine appears to have been a de- 
termining factor in tissue growth has been recorded by Evvard, 
Dox, and Guernsey in connection with their feeding experiments 
upon pregnant swine. Here a difference in the hair coats of 
the new-born pigs appeared to be due to the different intake of 
cystine in the food protein consumed by the mother, hair being 
rich in sulphur, and cystine the sulphur-bearing amino acid of 
the food. 

A so-called incomplete protein, i.e. one which when fed alone 
is quite inadequate to meet the requirements of protein metab- 
olism, may nevertheless contribute toward these requirements 
to an important degree and may even play a prominent part 
in promoting growth, as was strikingly demonstrated by Osborne 
and Mendel in experiments in which they added zein to a ration 
containing a small percentage of lactalbumin. (See Fig. 4, page 
66.) Here the addition of zein to the ration more than doubled 
the rate of growth. Still more recently McCollum, Simmonds, 
and Pitz, feeding rats on rations composed of a single grain 
with supplementary additions, find that gelatin supplements 
wheat proteins excellently though it apparently does not ap- 
* Journal of Biological Chemistry, Vol. 20, page 351. 



FOOD IN RELATION TO GROWTH 341 

preciably improve the proteins of maize or oats. Since gelatin, 
althougli lacking tyrosine and tryptophane is relatively rich in 
lysine, these results are interpreted as indicating that lysine is 
probably the limiting factor in wheat proteins but not in the 
proteins of the maize or of the oat kernel. 

In view of such evidence it is important to guard against the 
erroneous impression that incomplete proteins are useless for 
growth. The illustrations just given show that the growing 
organism may use such proteins to extremely good advantage ; 
but the " incomplete " proteins must not be permitted to dis- 
place the " complete " proteins to too great an extent if the 
young organism is to grow and develop at a fully normal rate. 

When growth is retarded by inadequate intake of protein 
or of a particular amino acid, the emaciated appearance char- 
acteristic of animals attempting to grow on an insufficient en- 
ergy intake is not to be expected. Osborne and Mendel have 
recorded numerous cases of suspension of growth of young 
rats, especially when kept on rations containing gliadin as a 
sole protein food. Here the inadequacy of the lysine intake 
results in retardation or even complete suspension of growth, 
but the animal may remain quite healthy and symmetrical. 
Moreover rats may be subjected to this type of stunting for a 
remarkably long time (even as long as would normally cover the 
entire growth period) and still retain their capacity to grow 
when given an adequate diet. 

In some cases*" after periods of suppression of growth, even 
without loss of body weight, growth may proceed at an exag- 
gerated rate for a considerable period. This is regarded as 
something apart from the rapid gains of weight in the repair or 
recuperation of tissue actually lost. Despite failure to grow 
for some time the average normal size may thus be regained be- 
fore the usual period of growth is ended." Statistical studies 

* Osborne, Mendel, Ferry, and Wakeman. A merican Journal oj Physiology, Vol. 
40, pages 16-20 (1916). 



342 CHEMISTRY OF FOOD AND NUTRITION 

on children also indicate that retardation in early growth can 
usually be made up by extra rapid growth later.* 

Mendel and Judson have studied the influence of different 
types of protein stunting upon the composition of the body in 
the case of the mouse. They find that when abundance of fat 
is furnished in the diet, but not enough protein to maintain 
normal growth, the percentage of fat in the animal becomes 
greater than when the food contains an adequate amount of 
protein with the same proportion of fat. They suggest that: 
" There seems to be a tendency to protect the limited amount 
of protein by increasing the available supply of fat in the body." 
" This does not occur when growth is arrested by lack of lysine, 
as in the use of gliadin as the only protein in the diet, since in 
this case the Umiting factor lies not in the amount but in the 
nature of the protein." 

(3) Ash Constituents 

Ash constituents have long been recognized as playing an 
important part in the growth of young animals and of these, 
as we have already seen, the elements most likely to be deficient 
are calcium, phosphorus, and iron. Infants (and young mam- 
mals generally) are born with a reserve store of iron usually 
sufficient to supply the growth requirement up to about the 
end of the normal suckhng period. At any time after this 
initial reserve supply has been used, the iron in the body will 
be found very largely localized in the blood. The blood con- 
stitutes less than 7 per cent of the weight of the body but con- 
tains more than 70 per cent of its iron content. Hence a deficit 
of iron becomes more noticeable in the blood than in the other 
tissues — growth may not cease but the child (or young animal) 
may grow anemic ; experiments illustrating this have been cited 
in the chapter on iron, and it has been shown that inorganic 
forms of iron are not of equal nutritive value with the organic 
* Mendel. Biochemical Bullclin, Vol. 3, page 167. 



FOOD IN RELATION TO GROWTH 



343 



forms which occur naturally in food materials. To an even 
greater extent than the iron is localized in the blood, the cal- 
cium of the body is localized in the bones ; it is estimated that 
the bones contain over 99 per cent of the body calcium. An 
inadequate supply of calcium in the food during growth retards 
the development and calcification of the bones. The calcium 
needed by the growing organism can be assimilated from inor- 
ganic forms. Both of these 
facts are illustrated by the 
experiment of raising pup- 
pies on meat with and with- 
out bones to gnaw as de- 
scribed in Chapter XI. It 
has also been found that the 
addition of calcium chloride 
and calcium carbonate to 
a basal ration of corn and 
common salt in the case of 
pregnant swine resulted in 
greater size, more vigor, 
bigger bone, and better 
general condition of the 
new-born pigs (Eward, 
Dox, and Guernsey). 

Bone development may 
also be interfered with by 
inadequacy of the phosphorus supply. Several investigators, 
in studying the effect of diet upon growth of bone, have found 
that the bones formed in a young animal kept on phosphorus 
poor diet are apt to be soft, spongy, and weak (of low breaking 
strength), and that this may be prevented by the simple addi- 
tion of calcium phosphate to the food. 

Since phosphorus is a prominent constituent not only of 
bones but of all the soft tissues as well, the effects of a phos- 




Time "> Months 
Fig. 13. — Efifect upon growth of adding to 
a diet otherwise adequate a salt mixture of 
such composition as to make the composition 
of the total ash similar to that of milk ash ; 
immediate resumption after entire suspension 
of growth.' Courtesy of Dr. E. V. McCoUum. 



344 



CHEMISTRY OF rOOD AND NUTRITION 



phorus deficiency may be far-reaching. In the experiments of 
Hart, McCollum, and Fuller, young pigs on phosphorus-poor 
food continued to grow for some time but finally developed not 
only the bone defects just noted but also weakness of the legs, 
stupor, and a more or less comatose condition accompanied by 
twitching of the muscles, dragging of the hind quarters, and 




Time in Months 
Fig. 14. — Growth at much less than half the normal rate through the greater 
part of the normal growth period, followed by accelerated growth upon adding a 
suitable salt mixture to the diet. Courtesy of Dr. E. V. McCollum. 

ultimately loss of weight and collapse. These effects were all 
prevented by simple addition of calcium phosphate to the food. 
Hart and McCollum record cases in which swine restricted 
to a ration of corn meal and corn gluten showed little or no 
growth, but began to make good growth upon addition to the 
food of such salts as to make the ash content of the ration similar 
to that of milk. 



FOOD IN RELATION TO GROWTH 



345 



McCollum, Simmonds, and Pitz have likewise shown that a 
defective inorganic content of the diet may also result in re- 
tardation or suspension of the general growth of the young 
animal, which may be followed by prompt resumption of growth 
(even at an accelerated rate so that the normal weight for the 
age may be regained) when a salt mixture is added such as to 
make the total ash of the ration similar in composition to milk 
ash (Figs. 13 and 14). 

(4) VlTAMINES OR FoOD HORMONES 

Osborne and Mendel (1913) found that the use of highly puri- 
fied salts in rations of isolated food substances resulted in less 
growth than when salts of only ordinary 
purity were fed. This suggested to them 
that other inorganic salts might be needed, 
and a ration containing very small addi- 
tions of salts of iodine, fluorine, manganese, 
and aluminum was fed with somewhat 
more favorable results than had attended 
the use of the usual (simpler) salt mix- 
ture ; but none of their diets composed 
entirely of pure substances gave as good 
results as the corresponding food mixtures 
in which " protein-free milk " was used, 
and they concluded that the latter was 
unquestionably superior to any purely arti- 
ficial food mixture. This superiority now 
seems to be attributable primarily to the soluble A " to a diet ade- 
presence in the " protein-free milk " of the quate in all other respects. 
"water soluble B," probably identical with °|"''^^*y ° 
the antineuritic " vitamine." If the latter 
is the case, the substance is not confined to milk but is fairly 
widely distributed among natural food materials. Less widely 
distributed is the other "essential accessory" furnished by milk, 




Time '" Months 
Fig. 15. — Effect upon 
growth of adding 



"fat 



346 



CHEMISTRY OF FOOD AND NUTRITION 



the so-called " fat soluble A," to the presence of which in butter * 
is attributed its marked growth-promoting property as shown 
independently by McCollum and Davis and by Osborne and 
Mendel. The latter find that in a diet containing " protein- 
free milk " and an adequate protein, 5 per cent of butter fat 
usually suffices to insure normal growth and in a few cases from 

I to 3 per cent has seemed 
sufficient. When butter 
fat is fractionally crystal- 
lized from alcohol the 
growth-promoting factor 
remains in the oil fraction , 
the fractions of higher 
melting point being in- 
effective. Lard and olive 
oil were also found in- 
efifective, while cod liver 
oil resembled butter fat 
in its growth-promoting 
property, and beef fat 
shows the same property 
to a less degree. Mc- 
Collum finds the same 
property in the fat of egg 
yolk and of animal organs such as the kidney, but in no com- 
mercial fat of vegetable origin thus far examined, although feed- 
ing experiments with whole grains and grain embryos indicate 
that their fats must carry appreciable amounts of this growth- 
promoting substance. He finds also, as noted earlier in the 
chapter, that the same " fat soluble A " (as demonstrated by 











A 






/ 




^r \ 




^Y 








/ 


"y 


"y" 


marks bir 
of young 


Th 


V 










/ ^ 


ithout 


"^y 


iter Soluhl 


, B" 




■ 













E 



Time '" Months 
Fig. 16. — Effect upon growth of adding 
" water soluble B " to an otherwise adequate 
diet. Courtesy of Dr. E. V. McCollum. 



♦According to McCollum, "fat soluble A" is about 30 times more soluble in 
fat than in w^ater. In milk about half of it is dissolved in the small volume of fat 
and about half in the large volume of water present. Skimmed milk is, therefore, 
not whullv devoid of this substance. 



FOOD IN RELATION TO GROWTH 347 

specially arranged feeding experiments) occurs in relative abun- 
dance in alfalfa and cabbage leaves and probably in green vege- 
tables and forage plants generally. The accompanying charts 
(Figs. 15 and 16) show the effects of presence or absence of A or 
B upon the growth curves of young rats. Recognition of the in- 
dependent need for each of these substances or groups of sub- 
stances is too recent for definite correlation of each with a dis- 
tinct type of stunting. Both " fat soluble A " and " water 
soluble B " are held to be essential for the maintenance of health 
as well as for growth. The fat soluble A appears to be dis- 
pensable, when maintenance alone is involved, for a somewhat 
longer period than is the water soluble B, which accounts for 
the polyneuritic symptoms in birds kept on polished rice diet 
and the cure of these symptoms by the feeding of extracts of 
foods rich in the water soluble B. Thus McCoUum and Ken- 
nedy find " that pigeons can be brought into the polyneuritic 
state by feeding a diet free from both the essential factors A 
and B, and can be completely cured and maintained in a normal 
condition for at least 35 days on the same diet which brought on 
the disease, plus the water extract of a foodstuff (rolled oats) 
on which rats cannot grow without the addition of butter fat, 
but on which they do grow when the latter is added." 

Dietary Deficiencies of Individual Articles of Food 

McCoUum and his associates are now applying the above 
conceptions to the study of the dietary deficiencies of individual 
articles of food. In a recent paper * they present their plan of 
investigation as follows : 

" If a single natural food product fails to nourish an animal 
adequately, it may be due to : (a) lack of suflScient protein, or 
to proteins of poor quality ; (b) an unsatisfactory mineral con- 
tent due either to inadequacy of certain elements in amount, or 

* McCoUum, Simmonds, and Pitz. Journal of Biological Chemistry, Vol. 25, 
pages 105, 132 (May, 1916). 



348 CHEMISTRY OF FOOD AND NUTRITION 

to unsatisfactory proportions among them ; (c) an inadequate 
supply of the fat soluble A ; (d) of the water soluble B ; (e) or 
some toxic substance contained therein. One, two, three, four, 
or all of these factors may operate in inducing nutritive dis- 
turbances. 

" It should be obvious that a systematic procedure in which 
we feed the substance under investigation supplemented with 
(a) pure protein only, (b) salt mixture additions only, (c) but- 
ter fat only, (d) extracts known to carry the water soluble B 
and as little else as is possible, will reveal whether the failure 
of nutrition involves one factor only, or more than one. If 
more than one factor is involved, a similar procedure, but with 
the addition of all possible combinations of pairs of the isolated 
food ingredients listed above, followed if need be by another 
series of feeding experiments in which animals are fed the 
natural foodstuff supplemented with three such uncomplicated 
additions, in all possible combinations, and if necessary another 
experiment in which all four additions are made, \vill give us 
results which make it possible to consider the components of 
our rations in an entirely new light. Provided the foodstuffs 
contain a toxic substance, special procedures will have to be 
devised for studying its effects. 

" Similar studies must also be made by this method of pro- 
cedure, with pairs of the important foodstuffs (food materials) 
in varying proportions, the variation of the mixture including 
sufficient range to reveal the degree to which the deficiencies 
of the protein mixture of one grain are corrected by the peculiar 
quantitative relationships among the amino acids yielded by 
the proteins of the other grain. The same may be said for the 
factors other than protein. In this way we shall become able 
to interpret the biological value of the. mixtures of natural 
foodstuffs which make up the rations which are in common use, 
in which the attempt is now made to make for safety through 
variety. We have carried our inquiry into the nature of the 



FOOD IN RELATION TO GROWTH 349 

dietary deficiencies of several natural products far enough to 
convince us of the practicability of this method of study." 

Following this general plan McCoUum and his associates 
have studied the dietary deficiencies of wheat, wheat embryo, 
rice, maize, oats, and beans. While some of the results thus 
obtained have already been cited, it may be well to summarize 
here the chief findings with reference to each of these food 
materials in succession. In all cases the experiments were 
chiefly upon rats. 

The wheat kernel when fed alone did not induce normal 
growth in the experimental animals. Addition of either (i) 
purified casein, (2) butter fat, or (3) a suitable salt mixture 
such as to make the total ash of the ration resemble milk ash in 
composition, was found to improve conditions to some degree 
in each case, but in no case did such a single addition result in 
normal growth. Neither could fully satisfactory results be 
secured by the addition to the wheat ration of any two of these 
three factors mentioned ; but when all three were added, the 
animals showed complete growth and normal reproduction. 
Hence McCollum concludes that the wheat kernel is deficient 
as a food (i) in the poor quality of its protein, (2) in that it 
furnishes an inadequate supply of " fat soluble A," (3) in that 
it has an unsatisfactory inorganic content. He also believes 
that when the diet is chiefly made up of the entire wheat kernel, 
including embryo, the possibility of a mild toxicity, due to a 
toxic constituent in the embryo, must also be reckoned with. 

Wheat embryo when fed alone did not induce growth although 
it is rich in proteins of high nutritive efficiency and in water 
soluble B, and not deficient in fat soluble A. It is deficient in 
its inorganic content; even so simple a modification as the 
addition of 2 per cent of calcium lactate to the wheat embryo 
diet may induce noteworthy growth where otherwise no growth 
takes place. To an important extent, according to these 
authors, the failure of rats and swine to grow on diets consisting 



350 CHEMISTRY OF FOOD AXD NUTRITION 

largely of wheat embryo is attributable to a toxic substance 
contained therein, which appears to be associated with the fat. 
Extraction of the fat by ether removes in great measure the 
toxicity of the embryo without necessarily making the food 
deficient in the fat soluble A. According to the authors the 
toxicity may be overcome by the simple addition of casein to 
the diet. That diet may greatly influence susceptibiHty to 
toxicity was reported by Hunt in 1910. Hunt found great 
differences in susceptibility to acetonitrile poisoning, which 
differences appeared to be due to diet alone.* 

Polished rice as a diet for growth was found to be deficient in 
four respects : (i) its protein content seemed too low for maxi- 
mum growth; (2) it contained inorganic elements in insuf- 
ficient amounts and also not in proper proportions ; (3) it was 
found deficient in fat soluble A ; (4) it lacked water soluble B. 

Maize when fed alone induced no appreciable growth, nor 
could a suitable diet be made by mixing the parts of the maize 
kernel in different proportions. The proteins of the maize 
kernel contain all the amino acids essential for growth, but it 
is held that the proportion of certain of them is such that 

* "In extreme cases mice after having been fed upon certain diets maj' recover 
from forty times the dose of acetonitrile fatal to mice kept upon other diets. It 
is, moreover, possible to alter the resistance of these animals at will and to overcome 
the effects of one diet by combining it with another. . . . The experiments with 
oats and oatmeal and eggs are of especial interest. In the earUer parts of this paper 
many experiments were quoted showing that a diet of oatmeal or of oats usually 
leads to a mark^ed resistance of mice to acetonitrile ; the experiments quoted in this 
section which show that the administration of certain iodine compounds with or 
subsequently to such a diet further increases this resistance, and the experiments 
previously reported showing that as far as the resistance toward acetonitrile is con- 
cerned iodine exerts its action through the thyroid gland, all point to the conclusion 
that the resistance caused by an oat diet is in part an effect e.xertcd upon the thyroid. 
This effect is obtained much more markedly and constantly with young, growing 
mice. From these experiments and considerations it seems very probable that it 
is possible to influence, in a specific manner, by diet, one of the most important 
hormones in the body ; this is a comparatively new principle in dietetics and one 
which may prove of much importance " (Hunt, The Effect of a Restricted Diet and of 
Various Diets upon the Resistance of Animals to Certain Poisons, pages 56, 73). 



FOOD IN RELATION TO GROWTH 351 

when this is the sole source of protein the growth is never more 
than about two thirds normal. The maize diet always requires 
the addition of a suitable salt mixture (or food of suitable ash 
content). Also the amount of fat soluble A is insufficient in 
maize to induce growth at the normal rate. Normal growth and 
reproduction, however, occurred when maize was supplemented 
by butter fat, purified casein, and a suitable salt mixture. 

The oat kernel, according to McCoUum's investigations, con- 
tains protein of poorer quality than either the maize or wheat 
kernel. When all other dietary factors are properly adjusted, 
nine per cent of oat protein in the diet serves to induce slow 
growth for a time, but never for more than about a month (ex- 
periments with rats). Casein, which serves as such an efficient 
adjunct to the wheat and maize proteins, does not seem to sup- 
plement oat protein in a very satisfactory manner ; a diet 
with 9 per cent of protein from the oat kernel and 10 per cent 
purified casein did not induce growth at a maximum rate as did 
similar combinations of casein with wheat and maize proteins. 
In this connection McCollum reports the unexpected finding 
that gelatin supplements the protein of the oat kernel more 
effectively than does casein. 

The ash constituents of the oat kernel must always be sup- 
plemented in order to induce growth. Fat soluble A is present 
in the oat kernel in very small amounts. The amount of water 
soluble B is adequate. Growth at more than half the normal 
rate may be obtained when the oat diet is supplemented by the 
addition of a suitable salt mixture and either butter fat or a 
suitable protein. When all three of these supplements are 
added, growth is normal but somewhat slow. McCollum be- 
lieves that excessive feeding of the oat kernel causes some 
injury to the animal. 

The -white bean, when fed as the chief component of the diet, 
gave results indicating that its proteins are of lower nutritive 
efficiency than those of the cereal grains. The bean protein 



352 CHEMISTRY OF FOOD AND NUTRITION 

can be supplemented by ihe addition of g per cent of casein to 
the diet. The inorganic content of the white bean is not such 
as to induce growth, but must be supplemented by a suitable 
salt mixture (or by food of a different ash content from that of 
the bean alone). The white bean seems to contain less of fat 
soluble A than do the cereal grains. It contains water soluble 
B in abundance. The bean diet appeared to exert an unfa- 
vorable effect in that animals fed on a diet containing a smaller 
proportion of beans (25 percent of the total food) seemed better 
nourished than those whose diet contained a larger proportion. 
It is suggested that beans may contain some unknown sub- 
stance which is harmful when taken in too large an amount ; 
or that the pressure of the intestinal gases resulting from fer- 
mentation of the hemicelluloses for which the higher animals 
have no digestive enzyme may result in a somewhat asphyxial 
condition of the intestinal wall, thus interfering with the normal 
processes of absorption and unfavorably affecting the general 
condition of nutrition. 

Seeds in general are held by McCollum to require supplement- 
ing in order to make a diet which will support normal growth 
and reproduction. As supplement to a diet consisting largely 
of the products of cereal grains or other seeds, milk is found to 
be especially effective. It is also found that while seeds are 
not effectively supplemented by other seeds, they may be sup- 
plemented by the leaves and probably also by the roots and 
tubers of plants so that it is feasible, if desired, to draw a bal- 
anced diet, adequate for all the requirements of growth and 
reproduction in an omnivorous animal, entirely from the prod- 
ucts of plants. Thus McCollum kept rats through four 
generations upon a carefully adjusted ration of maize, alfalfa, 
and cooked peas. Growth and reproduction were normal. 
The mothers successfully suckled young up to the normal age 
of weaning, after which they took the same food mixture as the 
adults. In this connection it is interesting to note that rats 



FOOD IN RELATION TO GROWTH 353 

which were free to make their own selection from a much 
greater variety of vegetable foods never grew beyond half the 
normal adult size. 

In practice milk is found to be most highly efficient as a sup- 
plement to diets consisting largely of seeds or their products: 
" The dietary should be built around bread and milk." The 
chemical constitution of its proteins and its high calcium and 
\itamine contents are all factors in the unique nutritive efficiency 
of milk, and make it possible for a moderate addition of milk 
to render adequate a diet otherwise composed entirely of seeds. 

Cotton-seed meal or flour * constitutes an abundant and con- 
centrated source of protein and energy which as yet has been 
but Httle utiHzed in human nutrition. This is doubtless largely 
because bad results have sometimes followed its use in stock 
feeding, leading to the general belief that it is somewhat toxic, 
at least when used in considerable quantities. Withers and 
Carruth succeeded in extracting from the kernels of the cotton- 
seed a substance, gossypol, which shows deleterious action when 
fed and to which the toxicity of raw cotton seed and of some 
cotton-Seed meals was attributed. This substance, however, 
is thermo-labile, and apparently is more or less completely de- 
stroyed by the heating to which cotton-seed meal or flour is 
ordinarily subjected in connection with the processes of crush- 
ing and pressing. Feeding experiments to determine whether 
the well-prepared cotton-seed meal or flour now available for 
human food has any appreciable toxicity, and to what extent 
it meets the nutritive requirements of normal growth and re- 
production, have recently been reported by Richardson and 
Green and by Osborne and Mendel. Richardson and Green, 
feeding a high-grade commercial cotton-seed flour, found that no 
evidence of toxicity appeared although this flour constituted 

* Cotton-seed flour is prepared by finely grinding, sifting, and perhaps also as- 
pirating the meal so that particles of lint, hulls, etc., are removed more completely 
than from the ordinary cotton-seed meal used in stock feeding. 
2 A 



354 CHEMISTRY OF FOOD AND NUTRITION 

45 to 50 per cent of the ration of albino rats through four 
successive generations or during 565 days of the life of an 
individual (about two thirds the entire normal Hfe span) ; 
that the cotton-seed flour met all protein requirements of main- 
tenance and growth, and when supplemented with protein-free 
milk and butter fat was able to support normal growth and re- 
production. They found that no better growth was induced, 
but more frequent reproduction with lower mortahty and more 
general well-being of animals were obtained when 5 per cent of 
casein was added to a diet containing 50 per cent cotton-seed 
flour with butter fat, protein-free milk, lard, and starch. Nor- 
mal growth and reproduction did not result from diets con- 
taining 50 per cent cotton-seed flour in which there was a lack 
of butter fat, protein-free milk, or both. On a diet containing 
fifty per cent cotton-seed flour with the addition of casein and 
butter fat, but with no mineral matter other than that from the 
cotton seed, rats grew normally and reproduced, but the second 
generation did not make quite normal growth. 

Osborne and Mendel also found the proteins of cotton-seed 
flour to be efficient in nutrition, not only when fed alone in 
relatively abundant amounts but also when used as supple- 
ments to maize protein. They obtained toxic effects from the 
feeding of cotton-seed kernels but not from the cotton-seed flour. 
Like Withers and Carruth they demonstrated that the harmful 
substance could be removed from the kernels by extraction with 
ether ; but the kernels can also be rendered harmless by steam- 
ing, which is a step in the usual commercial process of extracting 
the oil. The results of heating were, however, not altogether 
uniform and Osborne and Mendel suggest that undue heating 
may render the meal unpalatable or otherwise unsuitable for 
nutrition, in addition to destroying the original deleterious 
substance, and that these facts may help to explain the con- 
flicting evidence regarding the alleged suitabihty of different 
samples of commercial meals. 



FOOD IN RELATION TO GROWTH 355 

These recent investigations upon cotton-seed flour are worthy 
of careful study both because of the great economic importance 
of this material and because they illustrate well the application 
of modern methods of nutrition research to the solution of a 
long-standing problem regarding the utility of an abundant 
but relatively neglected food material. 

REFERENCES 

AcKROYD AND HoPKiNS. Feeding Experiments with Deficiencies in the 

Amino Acid Supply. Biochemical Journal, Vol. 10, page 551 (1916). 
Aron. Nutrition and Growth. Philippine Journal of Science, Vol. 6 B, 

pages 1-52 (191 i). 
Chittenden and Unt)erhill. The Production in Dogs of a Pathological 

Condition Closely Resembling Human Pellagra. American Journal of 

Physiology, Vol. 44, page 13 (191 7). 
Daniels and Nichols. The Nutritive Value of the Soy Bean. Journal 

of Biological Chemistry, Vol. 31, page 91 (19 17). 
Eward, Dox, and Guernsey. Effect of Calcium and Protein Fed Pregnant 

Swine upon the Size, Vigor, Bone, Coat, and Condition of the Offspring. 

American Journal of Physiology, Vol. 34, pages 312-325 (1914). 
Forbes.' Specific Effects of Rations upon the Development of Swine. 

Ohio Agricultural Experiment Station, Bull. 213 and 283 (1909 and 

1915)- 

GoETSCH. Influence of Pituitary Feeding upon Growth and Sexual Develop- 
ment. Johns Hopkins Ilospilal Bulletin, Vol. 27, page 29 (1916). 

Hart, Halpin, ant) McCollum. The Behavior of Chickens Fed Rations 
Restricted to the Cereal Grains. Journal of Biological Chemistry, 
Vol. 29, page 57 (February, 191 7). 

Hart and McCollum. Influence on Growth of Rations Restricted to the 
Corn or Wheat Grain. Journal of Biological Chemistry, Vol. 19, page 

373 (1914)- 

Hart, McCollum, and Fuller. The R6le of Inorganic Phosphorus 
in the Nutrition of Animals. Wisconsin Research Bulletin i ; Amer- 
ican Journal of Physiology, Vol. 23, page 246 (1908-1909). 

HLiRT, ]McCollum, Steenbock, and Humphrey. Physiological Effects 
upon Growth and Reproduction of Rations Balanced from Restricted 
Sources. Wisconsin Agricultural Experiment Station, Research Bull. 
17 (1912); Wisconsin Bull. 228, page 33; Journal of Agricultural 



356 CHEMISTRY OF FOOD AND NUTRITION 

Research, Vol. lo, page 175; and Proceedings of llic National Academy 
of Sciences, Vol. 3, page 374 (191 7). 

Hart, Miller, and McCollum. Further Studies on the Nutritive De- 
ficiencies of Wheat and Grain Mixtures and the Pathological Condi- 
tions Produced in Swine by their Use. Journal of Biological Chemislry, 
Vol. 25, page 239 (June, 1916). 

HoGAN. Corn as a Source of Protein and Ash for Growing Animals. Jour- 
nal of Biological Chemistry, Vol. 29, page 485 (191 7). 

Hopkins. Feeding Experiments Illustrating the Importance of Accessory 
Factors in Normal Dietaries. Journal of Physiology, Vol. 44, page 
425 (1912). 

LusK. Science of Nutrition, Third Edition, Chapters 13 and 14. 

McCoLLUM. The Value of the Proteins of the Cereal Grains and of Milk 
for Growth in the Pig, and the Influence of the Plane of Protein In- 
take on Growth. Journal of Biological Chemistry, Vol. 19, page 323 
(November, 191 4). 

McCoLLUM. The Supplementary Dietary Relationships among Our 
Natural Foodstuffs. Journal of the American Medical Association, 
Vol. 68, page 1379 (May 12, 191 7). 

McCoLLUM AND Davis. The Substance in Butter Fat Which Exerts a 
Stimulating Influence on Growth. Journal of Biological Chemistry, 
Vol. 19, page 245 (October, 1914). 

McCoLLUM AND Davis. Influence of the Plane of Protein Intake on Growth. 
Journal of Biological Chemistry, Vol. 20, page 415 (1915). 

McCollum and Davis. Nutrition with Purified Food Substances. Jour- 
nal of Biological Chemistry, Vol. 20, page 641 (.A.pril, 1915). 

McCollum and D.wis. Influence of Certain Vegetable Fats on Growth. 
Journal of Biological Chemislry, Vol. 21, page 179 (May, 1915). 

McCollum and Davis. Influence of Mineral Content of the Ration on 
Growth and Reproduction. Journal of Biological Chemislry, Vol. 21, 
page 615 (July, 1915)- 

McCollum and Davis. The Nature of the Dietary Deficiencies of Rice. 
Journal of Biological Chemislry, Vol. 23, page 181 (November, 1915). 

McCollum and Davis. The Essential Factors in the Diet during Growth. 
Journal of Biological Chemislry, Vol. 23, page 231 (November, 1915). 

McCollum and Simmonds. A Biological Analysis of Pellagra-Producing 
Diets. Journal of Biological Chemistry, Vol. 31, pages 29 and 181; 
Vol. 32, page 347 (1917). , 

McCollum, Simmonds, and Pitz. The Nature of the Dietary Deficiencies 
of the Wheat Embryo. Journal of Biological Chemistry, Vol. 25, page 
105 (May, 1916). 



FOOD IN RELATION TO GROWTH 357 

McCoLLUM, SiMMONDS, AND PiTZ. The Relation of the Unidentified Diet- 
ary Factors, the Fat-soluble A, and Water-soluble B, of the Diet to the 
Growth-promoting Properties of Milk. Journal of Biological Chemistry, 
Vol. 27, page 33 (October, 1916). 

McCoLLXJM, SiMMONDS, AND PiTz. The Vegetarian Diet in the Light of 
Our Present Knowledge of Nutrition. A mcrican Journal of Physiology, 
Vol. 41, page 333 (September, 1916). See also Journal of Biological 
Chemistry, Vol. 30, page 13 (May, 1917)- 

McCoLLUM, SiMMONDS, AND PiTz. The Distribution in Plants of the Fat 
Soluble A, the Dietary Essential of Butter Fat. American Journal of 
Physiology, Vol. 41, page 361 (September, 1916). 

McCoLLUM, SiMMONDS, AND PiTz. Dietary Deficiencies of the Maize 
Kernel. Journal of Biological Chemistry, Vol. 28, page 153 (December, 
1916). 

McCoLLUM, SiMMONDS, AND PiTZ. The Effects of Feeding the Proteins of 
the Wheat Kernel at Different Planes of Intake. Journal of Biological 
Chemistry, Vol. 28, page 211 (December, 1916). 

McCoLLUM, SiMMONDS, AND PiTZ. Is Lysine the Limiting Amino Acid in 
the Proteins of the Wheat, Maize, or Oat Kernel? Journal of Bio- 
logical Chemistry, Vol. 28, page 483 (January, 1917)- 

McCoLLUM, SiMMONDS, AND PiTz. The Nature of the Dietary Deficiencies 
of the Oat Kernel. Journal of Biological Chemistry, Vol. 29, page 341 
(March, 191 7). 

McCoLLUM, SiMMONDS, AND PiTZ. The Dietary Deficiencies of the White 
Bean {Phaseolus vulgaris). Ibid., Vol. 29, page 521 (April, 1917)- 

McCrudden. Nutrition and Growth of Bone. Transactions of the 15th 
International Congress of Hygiene and Demography, Washington, 191 2. 

Mendel. Viewpoints in the Study of Growth. Biochemical Bulletin, 
Vol. 3, page 156 (January, 1914)- 

Mendel. Nutrition and Growth. The Harvey Lectures, Series 10, 
1914-1915. 

Mendel. Abnormalities of Growth. American Journal of the Medical 
Sciences, Vol. 153, page i (January, 1917). 

Mendel and Judson. Some Interrelations between Diet, Growth, and the 
Chemical Composition of the Body. Proceedings of the National 
Academy of Sciences, Vol. 2, page 692 (December, 1916). 

Mendel and Osborne. Growth. Journal of Laboratory and Clinical 
Medicine, Vol. i, page 211 (January, 1916). 

Osborne and Mendel. Feeding Experiments with Isolated Food Sub- 
stances. Carnegie Institution of Washington, Publication No. 156, 
Parts I and II (191 1). 



358 CHEMISTRY OF FOOD AND NUTRITION 

Osborne and Mentjel. R6le of Gliadin in Nutrition. Journal of Biologi- 
cal Chemislry, Vol. 12, pages 473-510 (1912). 

Osborne and Mendel. Influence of Butter Fat on Growth. Journal of 
Biological Chemislry, Vol. 16, pages 423-437 (1913). 

Osborne and Mendel. The Influence of Cod Liver Oil and Some Other 
Fats on Growth. Journal of Biological Chemislry, Vol. 17, page 401 
(April, 1914). 

Osborne and Mentjel. Relation of Growth to the Chemical Constituents 
of the Diet. Journal of Biological Chemislry, \'o\. 15, pages 311-326 

(1913)- 

Osborne and Mendel. Amino Acids in Nutrition and Growth. Journal 
of Biological Chemislry, Vol. 17, pages 325-349 (1914). 

Osborne and Mendel. Nutritive Properties of Proteins of the Maize 
Kernel. Journal of Biological Chemislry, Vol. 18, pages 1-16 (1914). 

Osborne and Men-del. The Comparative Nutritive Value of Certain 
Proteins in Growth, and the Problem of the Protein Minimum. Jour- 
nal of Biological Chemistry, Vol. 20, page 351 (1915). 

Osborne and Mentjel. Resumption of Growth after Long-Continued 
Failure to Grow. Journal of Biological Chemislry, Vol. 23, page 439 
(December, 1915). 

Osborne and Mentjel. The Stability of the Growth-Promoting Sub- 
stance of Butter Fat. Journal of Biological Chemislry, Vol. 24, page 37 
(January, 1916). 

Osborne ant) Mentjel. Acceleration of Growth after Retardation. Atner- 
ican Journal of Physiology, Vol. 40. page 16 (March, 1916). 

Osborne and Mentjel. The Amino Acid Minimum for Maintenance and 
Growth, as exemplified by further experiments with lysine and trjpto- 
phan. Journal of Biological Chemislry, Vol. 25, page i (May, 1916). 

Osborne and Mendel. The Growth of Rats upon Diets of Isolated Food 
Substances. Biochemical Journal, Vol. 10, page 534 (1916). 

Osborne and Mentjel. The Relative Value of Certain Proteins and Pro- 
tein Concentrates as Supplements to Corn Gluten. Journal of Bio- 
logical Chemislry, Vol. 29, page 69 (February, 191 7). 

Osborne and Mendel. Nutritive Factors in Animal Tissues. Journal 
of Biological Chemislry, Vol. 32, page 309 (191 7). 

Osborne and Mendel. The Use of Soy Bean as Food. Journal of Bio- 
logical Chemistry, Vol. 32, page 369 (191 7). 

Osborne, Mentjel, and Ferry. The Eflect of Retardation of Growth 
upon the Breeding Period and Duration of Life of Rats. Science, Vol. 
45, page 294 (1917)- 

Pearl. Effect of Feeding Pituitary Substance and Corpus Luteum on 



FOOD IN RELATION TO GROWTH 359 

Egg Production and Growth. Journal of Biological Chemistry, Vol. 24, 
page 123 (February, igi6). 

Rettger. Influence of Milk Feeding on Mortality and Growth. Journal 
of Experimental Medicine, Vol. 21, page 365 (19 15). 

Richardson and Green. Nutrition Investigations upon Cotton-seed Meal. 
Journal of Biological Chemistry, Vol. 25, page 307 (1916); Vol. 30, 
page 243; Vol. 31, page 379 (1917)- 

Robertson. (Experimental Studies of Growth and the Growth-control- 
ling Substance of the Pituitary Body.) Journal of Biological Chemistry, 
Vol. 24, pages 347, 2,(^3^ 385. 397, 409; Vol. 25, pages 625, 647, 663; 
Vol. 27, page 393 (1916). 

Waters. The Capacity of Animals to Grow under Adverse Conditions. 
Proceedings of the Society for the Promotion of Agricultural Science, Vol. 
29, page 3 (1908). 

Waters. Influence of Nutrition on Animal Form. Proceedings of the So- 
ciety for the Promotion of Agricultural Science, Vol. 30, page 70 (1910). 



CHAPTER XIV 

DIETARY STANDARDS AND THE ECONOMIC USE OF 

FOOD 

The General Problem of a Dietary Standard 

It is sometimes asked whetlier a normal appetite does not 
indicate, as well as can any dietary standard, the amount of 
food which is desirable for an individual in any given circum- 
stances. 

In considering such a question we shall hardly expect the 
phrase " amount of food " to indicate equally the energy 
value, the protein content, the content of each of the necessary 
chemical elements, and each of the unidentified dietary essentials 
A and B (or fat soluble and water soluble " vitamines ")• Since 
different articles of food vary greatly in the relative amounts 
of the various nutrients which they contain, some one aspect 
of food value must be chosen as a basis in order to give definite 
meaning to the phrase " amount of food." Inasmuch as the 
most prominent of the nutritive requirements is the need for 
energy, and the yielding of energy is the one function in which 
practically all articles of food take part, it is logical to expect 
that " amount of food " will more nearly express number of 
calories than any other one factor of food value or nutritive 
requirement. Observation confirms this impression and shows 
that men or other animals when eating varied food under the 
unrestricted guidance of hunger and appetite tend to take such 
quantities as are proportioned to the energy requirement 

360 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 36 1 

whether or not this amount meets also the requirements as 
to each of the sixteen chemical elements known to be necessary 
in nutrition. 

If then hunger and appetite be regarded as guides, primarily, 
to the eating of the right amount of food to meet the energy 
requirement, we may determine their adequacy in any given case 
by the fatness of the person concerned, since excess of fuel food 
of whatever kind can contribute to the storage of body fat. 

If from year to year the body keeps in good condition for 
its work and maintains a fairly constant weight which bears 
such a proportion to the height as to show that a proper amount 
of fat is being carried, it is reasonably certain that the amount 
(fuel value) of food eaten in the course of the year is substantially 
that which is suited to the degree of activity maintained. If, 
however, by following the appetite, one becomes unduly stout 
or unduly thin, or does not get sufficient fuel for the energy 
required for the day's work, or is annoyed by digestive disturb- 
ances indicative of improper feeding, it is certain that the 
appetite is in this case not a perfect standard. Still more often 
will the individual appetite prove an inadequate guide to such 
a quantitative combination of the different types of food as 
shall lead to a well-balanced intake of each of the many essential 
food constituents. Here the customs and traditions which 
govern the food economics of the household and which un- 
doubtedly to some extent reflect the accumulated experience 
of the race serve an extremely important purpose in checking 
the caprices of the palate and guiding the individual into food 
habits which are more likely to conform to actual needs than 
are the dictates of the individual appetite. But the fullest 
appreciation of the value of household and social traditions 
in the formation of good dietary habits does not justify the 
conclusion that such traditions will always lead to the best 
results, either physiologically or economically. Even if these 
traditions represented the experience of past generations to 



362 CHEMISTRY OF FOOD AND NUTRITION 

the fullest imaginable extent, they could not be expected to 

guide us in the use of foods which were not available to our 

predecessors but have now within a generation become a common 

part of the dietary. Nor is it reasonable to suppose that dietary 

habits adapted to people engaged chiefly in outdoor occupations 

under frontier conditions will be equally suited to the sedentary 

city worker of to-day. Under modern conditions scientific 

dietary standards, based on a knowledge of food chemistry 

and nutritive requirements such as the preceding chapters 

have attempted to give, constitute the most rational guide to 

the formation of hygienic and economic habits in the use of food. 

The earliest attempts to set dietary standards in terms of 

nutrients were those of the German physiologists, among whom 

the most influential was Voit. He suggested as a proper 

daily allowance of foodstuffs for a man at moderate muscular 

work : 

Protein, 118 grams. 

Fat, 56 grams. 

Carbohydrates, 500 grams. 

This dietary would have a fuel value of approximately 3000 
Calories. The allowance of 118 grams of protein, which has 
since provoked considerable discussion, is said to have been 
based upon the average protein metabolism of many laboring 
men who were living apparently upon unreetricted diet, so 
that it was practically the result of dietary study. In the 
division of the remaining calories between fat and carbohydrate, 
Voit made the allowance of fat low and of carbohydrates high 
in order to cheapen the dietary. 

In England, Playfair recommended as a standard for a man 
at moderate work : 

Protein, 119 grams. 

Fat, 51 grams. 

Carbohydrates, 531 grams. 



DIETARY STANDARDS AND ECONOINIIC USE OF FOOD 363 

This would yield 3060 Calories and is evidently based quite 
directly upon Voit's recommendations. 

In France, Gautier has proposed as a standard for men with 
Uttle muscular work : 

Protein, 107 grams. 

Fat, 65 grams. 

Carbohydrates, 407 grams. 

This allowance of nutrients — which is based in part upon 
carbon and nitrogen balance experiments, in part upon studies 
of French famiUes selected as typical, and in part upon the 
statistics of food consumed in Paris for a period of ten years — 
would supply 2630 Calories. 

In America, dietary standards have been discussed chiefly by 
Atwater, Chittenden, and Langworthy. Atwater, in his later 
writings,* ceasing to make distinction between fats and carbohy- 
drates as sources of energy in ordinary dietaries, but making 
allowances for different degrees of muscular activity, rec- 
ommended the following standards: 



Standards for 


Protein, 
Grams 


TuEL Value, 
Calories 


Man at hard muscular work 

Man at moderately active muscular work 

Man at sedentary or woman with moder- 
ately active work - 

Man without muscular exercise or woman 
at light to moderate work 


150 
125 

100 
90 


4150 
3400 

2700 
2450 



That these standards were not intended simply as expressions 
of the actual needs of the body is plainly shown by the allowance 
of 150 grams of protein for a man at hard work, as against 100 
grams for a sedentary man. By his own experiments with men 
at rest and at work in the respiration calorimeter Atwater had 

* Farmers' Bulletin No. 142, U. S. Department of Agriculture. Also Fifteenth 
Annual Report Ag,rkullural Experiment Sldtion, Starrs, Conn., 1903. 



3^4 



CHEMISTRY OF FOOD AND NUTRITION 



demonstrated that muscular work need not increase protein 
metabolism, if a sufficient amount of fuel be provided in the 
form of carbohydrates and fats. Hence, when, in providing for 
muscular work, he proposes to increase the protein in practically 
the same ratio as the calories, the idea evidently is not that such 
an increase is necessary, but simply that it was considered 
advisable on general grounds not to alter very greatly the 
nature of the diet in increasing its amount. 

Langvvorthy's Compilation of Results of Dietary Studies 



Occupation of Head of Family 



United States : 

Man at very hard work (average 19 studies) . 

Farmers, mechanics, etc. (average 162 studies) 

Business men, students, etc. (average 51 studies) 

Inmates of institutions, little or no muscular 
work (average of 49 studies) 

Very poor people, usually out of work (average 

of 15 studies) 

Canada: Factory hands (average 13 studies) 

England : Workingmen 

Scotland : Workingmen 

Ireland : Workingmen 

Germany : Workingmen 

Professional men 

France : Men at light work 

Japan : Laborers 

Professional and business men 

China : Laborers 

Egypt : Native laborers 

Congo : Native laborers 



Food per Man* 


PER 


Day 


Protein, 


Fuel value, 


Grams 


Calories 


177 


6000 


100 


3425 


106 


3285 


86 


2600 


69 


2100 


108 


3480 


89 


2685 


108 


3228 


98 


3107 


134 


3061 


III 


2511 


no 


2750 


118 


4415 


87 


2igo 


91 


3400 


112 


2825 


108 


2812 



*In calculating these results it is assumed that women consume o.S as much 
food as men, and children of different ages from 0.3 to 0.8 as much as the man 
of the family. 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 365 

In explanation of the liberality of his standards Atwater 
suggested that " the standard must vary not only with the 
conditions of activity and environment, but also with the nutri- 
tive plane at which the body is to be maintained. A man 
may live and work and maintain bodily equilibrium on either 
a higher or a lower nitrogen level, or energy level. One essential 
question is, What level is most advantageous? The answer 
to this must be sought, not simply in metabolism experiments 
and dietary studies, but also in broader observations regarding 
bodily and mental efficiency and general health, strength, and 
welfare." 

Langworthy, maintaining a similar point of view, has collected 
the data of large numbers of dietaries believed to be fairly 
representative of the food habits of people of different occupa- 
tions in the United States and other countries, and stated them 
in terms of protein and calories per man per day with the 
results shown on the preceding page, 

Langworthy concludes that the results obtained, the world 
over, for persons of moderate activity, " do not differ very 
markedly from a general average of 100 grams of protein and 
3000 Calories of energy, and that it is fair to say that, although 
foods may differ very decidedly, the nutritive value of the 
diet in different regions and under different circumstances is 
very much the same for a like amount of muscular work." 
He also points out that in some cases this may not be apparent 
until allowance is made for differences in body weight. Thus 
he estimates the average weight of the Japanese professional 
and business men at 105 pounds, so that their food consumption 
of 87 grams protein and 2190 Calories corresponds to 105 grams 
protein and 3120 Calories for a man of 150 pounds, which agrees 
well with the American average for similar employment. 

As a standard for men with more muscular activity, such 
as mechanics at moderately active work, Langworthy sug- 
gests 3500 Calories including 105 grams of protein. 



366 CHEMISTRY OF FOOD AND NUTRITION 

Chittenden differs from those whose standards have been 
quoted in giving almost no weight to the results of dietary 
studies, holding that these serve chiefly as a measure of self- 
indulgence, and that the true measure of what the body will 
most profitably use is to be found in the results of experi- 
ments upon the protein metabolism, such as have been de- 
scribed in Chapter VIII. On the basis of these experiments 
he proposes as a standard allowance for the man of 70 kilograms 
body weight, 60 grams of protein and 2800 Calories per day. 
For business and professional men such as Chittenden evidently 
has in mind, the allowance of 2S00 Calories is in substantial 
agreement with earher estimates. Sixty grams of protein for a 
man of 70 kilograms is, however, decidedly lower than any 
standard previously current. 

Energy Allowances for Adults 

It has been shown in a previous chapter that different normal 
individuals of similar age and physique are substantially alike 
in their energy requirement when performing equivalent amounts 
of muscular work, and that it is primarily the muscular activity, 
and not personal idiosyncrasy or the amount of food eaten, which 
determines the amount of energy transformed in the body. A 
dietary standard of high fuel value, and designed to maintain 
metaboHsm on a high energy level, provides, therefore, primarily 
for a large amount of muscular work. If this work is not 
performed and the food continues to be eaten and digested, 
we may expect to find a storage of fuel in the body chiefly in 
the form of fat, and this is true whether the surplus food eaten 
is carbohydrate, fat, or protein. Thus the store of body fat 
which a person carries is the most reliable indication as to 
whether the amount of food habitually eaten is or is not properly 
adjusted to the work performed. The storage of fat does, 
however, in itself modify the food requirement. While it is 
true, as has been shown, that, as between a lean and a fat man 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 367 

having the same weight, the lean man will have the greater food 
requirement, yet it is also true that when any given man becomes 
fat, his increased size of body calls for increased metaboHsm of 
energy. The work involved in walking, for example, will 
increase in proportion to the weight moved {i.e. to the weight 
of the body as a whole) ; and the work of respiration will in- 
crease about in proportion to the weight of that part of the body 
which must be moved with the expansion and contraction of the 
lungs; while, if fat is deposited in such a way as to interfere 
directly with the free play of the muscles, there may be an 
actual lowering of muscular efficiency, so that a larger expendi- 
ture of energy may be required in order to produce a given 
amount of work. If the liberal diet is continued and the 
digestion remains normal, the storage of fat will continue until 
it raises the energy expenditure of the body to a point where the 
food is no longer in excess. If the store of fat carried when this 
point is reached is excessive, the fuel value has been too high ; 
if the store of fat is not excessive, the fuel value of the diet, 
although greater than would have been necessary to maintain 
the body at its former weight, has not been too high, and the 
body has acquired an asset whose utility may not always be 
recognized in health, but which may be of great value in case 
of accident, illness, or exposure. 

Opinions differ somewhat as to the desirable degree of fatness 
as indicated by the relation of height to body weight. 

Hill * estimates the average height at 25 years of age as 
5 feet 3 inches for women and 5 feet 8 inches for men, and the 
corresponding average weights as 119 and 150 pounds respec- 
tively. He considers that variations of 10 to 15 per cent above 
or below the average should be considered normal. According 
to this estimate the woman of 5 feet 3 inches should weigh 
not less than 102-107, ^or more than 131-136 pounds, and the 
man of 5 feet 8 inches not less than 128-135, nor more than 

* Recent Advances in Physiology and Biochemistry, 



368 



CHEMISTRY 01" FOOD AND NUTRITION 



165-173 pounds. These figures arc exclusive of clothing. Hill 
considers as " fal " those persons whose weight exceeds the 
average by 15 to 30 per cent, and as " over fat " those who 
exceed by more than 30 per cent, i.e. over 155 pounds for a 
woman 5 feet 3 inches or over 195 pounds for a man 5 feet 8 
inches. 

Symonds has published * the average relation of height to 
weight in both men and women at different ages, as computed 
from the records of accepted apphcants for life insurance in 
the United States and Canada. The results are found in the 
following tables; that for men being based on 74,162 and that 
for women on 58,855 cases. In all these cases the height in- 
cludes shoes and the weight includes ordinary clothing. 



Symonds's Table of Height and Weight for Men at Different Ages 

BASED ON 74,162 accepted APPLICANTS FOR LIFE INSURANCE 

{Medical Record) 



Agds 


iS-24 


25-29 


30-34 


3S-39 


40-44 


45-49 


50-54 


55-59 


60-64 


65-69 


5 ft. 


in. 


120 


125 


128 


131 


133 


134 


134 


134 


131 






I in. 


122 


126 


129 


131 


134 


136 


136 


136 


134 






2 in. 


124 


128 


131 


133 


136 


138 


138 


138 


137 






3 in. 


127 


131 


134 


136 


139 


141 


141 


141 


140 


140 




4 in. 


131 


135 


13H 


140 


143 


144 


145 


145 


144 


143 




5 in. 


134 


138 


141 


143 


146 


147 


149 


149 


148 


147 




6 in. 


13H 


142 


145 


147 


150 


151 


153 


153 


153 


151 




7 in. 


142 


147 


150 


152 


155 


156 


158 


158 


158 


156 




8 in. 


146 


151 


154 


157 


160 


161 


163 


163 


163 


162 




g in. 


150 


155 


159 


162 


165 


166 


167 


168 


i68 


168 




10 in. 


1 54 


159 


164 


167 


170 


171 


172 


173 


174 


174 




1 1 in. 


159 


164 


169 


173 


175 


177 


177 


178 


180 


180 


6 ft. 


in. 


i6s 


170 


175 


179 


180 


183 


182 


183 


185 


18S 




I in. 


170 


177 


181 


185 


186 


189 


188 


189 


189 


189 




2 in. 


176 


184 


188 


192 


194 


196 


194 


194 


192 


192 




3 in. 


181 


190 


195 


200 


203 


204 


201 


198 







* Medical Record, September 5, 1908; and McClurc's Magazine, January, igog. 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 369 



Symonds's Table of Height and Weight for Women at Different 

Ages 

based on 58,855 accepted applicants for life insurance 

(McClure's Magazine) 



Ages 


1S-19 


20-24 


25-29 


30-34 


35-39 


40-44 


45-49 


so-54 


55-59 


60-64 


4 


ft. II in. 


III 


"3 


115 


117 


119 


122 


125 


128 


128 


126 


5 


ft. in. 


113 


114 


117 


119 


122 


125 


128 


130 


131 


129 




I in. 


"5 


116 


118 


121 


124 


128 


131 


133 


134 


132 




2 in. 


117 


118 


120 


123 


127 


132 


134 


137 


137 


136 




3 in. 


120 


122 


124 


127 


131 


135 


138 


141 


141 


140 




4 in. 


123 


125 


127 


130 


134 


138 


142 


145 


14s 


144 




5 in. 


125 


128 


131 


13s 


139 


143 


147 


149 


149 


148 




6 in. 


128 


132 


135 


137 


143 


146 


151 


153 


153 


152 




7 in. 


132 


135 


139 


143 


147 


150 


154 


157 


156 


IS'? 




8 in. 


136 


140 


143 


147 


151 


155 


158 


161 


161 


160 




9 in. 


140 


144 


147 


151 


15s 


159 


163 


166 


166 


165 




10 in. 


144 


147 


151 


15s 


159 


163 


167 


170 


170 


169 



From a study of the records of body weight in relation to 
the mortahty records Symonds concludes that among young 
people the greatest vitality coincides with a weight somewhat 
above the accepted average, while with middle-aged and 
elderly people a condition of slightly less than average fatness 
is most favorable to vitality and longevity. Another way of 
stating the same facts is: That the average of healthy men 
and women keep themselves slightly too thin while young, 
and allow themselves to grow slightly too stout as they grow 
older. 

Evidently, however, the optimum is very near the average 
of the accepted applicants as shown in the tables, and Symonds 
uses these figures as standards in his computations and dis- 
cussions of the influence of overweight and underweight on 
longevity and on mortality from specific diseases. Symonds's 
data therefore support the opinion that the average degree of 



370 CHEMISTRY OF FOOD AND NUTRITION 

fatness of healthy American people is just about the most 
advantageous fatness for them to maintain. Whatever we 
accept as the ideal relation of weight to height, it is obvious 
that the proper standard for fuel value of the diet is that which 
will preserve the desired degree of fatness while sustaining the 
desired amount of activity. If good authorities differ in 
standards for fuel value, it is because, consciously or uncon- 
sciously, they contemplate different amounts of muscular 
activity or the maintenance of a different physique. 

That the amount of food required per day to maintain a 
healthy adult at the desired body weight will vary considerably 
with age and size and enormously with extremes of muscular 
activity has already been explained at some length in Chapter 
VII and need not be discussed further here. Unless it is desired 
to increase or decrease the body weight, the optimum energy 
intake of the healthy adult will be that which coincides with the 
total energy expenditure; in other words the "standard" 
and the " requirement " will in this case be the same. 

Energy Allowances for Children 

Food allowances or dietary standards for children differ 
from those for adults in that they must provide not only for all 
expenditures but also for growth. Recently a considerable 
number of accurate measurements of energy expenditure of 
children have been made — especially of infants in the first 
year of life and of boys twelve and thirteen years old. These 
data whether obtained by the method of direct or indirect 
calorimetry give precise information as to the energy output 
at the time of the experiment, but naturally the observations 
cannot cover the entire 24 hours of the day, nor can experiments 
of a few hours' duration give any direct information as to how 
much the intake must exceed the output in order to provide 
amply for a normal rate of growth. Observations of the un- 
restricted food consumption (ordinary dietary studies) of 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 371 

healthy children who are making normal growth, and nitrogen 
balance experiments which show both gain in weight and storage 
of nitrogen (growth of protein tissue) may be expected to furnish 
evidence of some value though of a somewhat inferential nature. 
As a result of compilation and study of all available data whether 
of dietary studies, nitrogen balance experiments, observations 
of the respiratory exchange, or direct measurements of energy 
output, the following standards are suggested: 

Food Allowances for Healthy Children (Gillett) 



Age 


Calories per Day 


Years 


Boys 


Girls 


Under 2 


900-1200 


900-1 200 


2-3 


1000-1300 


980-1280 


3-4 


I 100-1400 


1060-1360 


4-S 


1200-1500 


I 140-1440 


5-6 


1300-1600 


1 2 20-1 5 20 


6-7 


1400-1700 


1300-1600 


7-8 


1500-1800 


I 380-1 680 


- 8-9 


1600-1900 


1460-1760 


9-10 


I 700-2000 


I 5 50-1 850 


lO-II 


1900-2200 


1650-1950 


11-12 


2100-2400 


1750-2050 


12-13 


2300-2700 


1850-2150 


13-14 


2500-2900 


1950-2250 


14-15 


2600-3100 


2050-2350 


15-16 


2700-3300 


2150-2450 


16-17 


2 700-3400 


2250-2500 



In earlier allowances no distinction was made between boys 
and girls below ten years of age. The averages of recorded 
data show, however, a slightly higher energy exchange (or 
metabolism) in boys than in girls of the same age, though 
the difference is often less than the range allowed to cover 
differences of size and activity at a given age. Beyond 10 



372 



CHEMISTRY OF FOOD AND NUTRITION 



years of age, the energy exchange in boys evidently increases 
more rapidly than in girls, probably because of their greater 
restlessness and muscular activity through this period of de- 
velopment and their greater average rate of growth during 
and after the fifteenth year. 

In this connection the accompanying table adapted from that 
of Manny based on data from Holt, Burt, and Boas is of interest. 

Average Weights and Rates of Growth of Boys and Girls at 
Different Ages (Manny) 







Boys 






Gtrls 




Age 


















Weight 


Increase 


Weight 


Increase 




Kgms. 


Lbs. 


Per 

Year 
Lbs. 


Per 

Week 
Grams 


Kgms. 


Lbs. 


Per 

Year 
Lbs. 


Per 
Week 

Grams 


At birth . . 


3-43 


7-55 






3-25 


7.16 






6 months . . 


7.27 


16.00 


16.90 


147 


7-05 


15-50 


16.68 


145 


I year . . 


9-32 


20.50 


9.00 


78 


9.00 


19.80 


8.60 


75 


2 years . . 


12.05 


26.50 


6.00 


52 


"-59 


25-50 


S-70 


50 


3 years . . 


14.18 


31-20 


4.70 


41 


13-63 


30.00 


4-50 


39 


4 years ' . . 


15-91 


35-00 


3-80 


33 


15-45 


34-00 


4.00 


35 


5 yr. 6 mo. 


18.73 


41.20 


4-13 


36 


18.09 


39-80 


3.87 


34 


6 yr. 6 mo. 


20.55 


45.20 


4.00 


35 


19-73 


43-40 


3-60 


31 


7 yr. 6 mo. 


22.50 


49-50 


4-30 


38 


21.68 


47.70 


4-30 


38 


8 yr. 6 mo. 


24.77 


54-50 


5.00 


44 


23-86 


52.50 


4.80 


42 


9 yr. 6 mo. 


27.09 


59.60 


5.10 


45 


26.09 


57-40 


4.90 


43 


lo yr. 6 mo. 


29-73 


65.40 


5-80 


51 


28.59 


62.90 


5-50 


48 


II yr. 6 mo. 


32.14 


70.70 


5-30 


46 


31-59 


69.50 


6.60 


S8 


12 yr. 6 mo. 


34-95 


76.90 


6.20 


54 


35-77 


78.70 


9.20 


80 


13 yr. 6 mo. . 


38.55 


84.80 


7-90 


69 


40.32 


88.70 


10.00 


87 


14 yr. 6 mo. 


43-27 


95-20 


10.40 


91 


44.68 


98.30 


9.60 


84 


15 yr. 6 mo. 


48.82 


107.40 


12.20 


107 


48-50 


106.70 


8.40 


73 


16 yr. 6 mo. 


S5-00 


121.00 


13.60 


119 


51.02 


112.30 


5.60 


49 



Children, like adults, will vary in muscular activity and this 
will influence their energy requirements irrespective of other 
conditions. Among other conditions to be considered are 
differences in size and physical development among children 



DIETARY STANDARDS AND ECONOI^IIC USE OF FOOD 373 

of the same age and sex. Children of more than average size, if 
normally active and not over-fat, will require somewhat more 
food than an average child of the same age. An estimate of 
energy requirement per unit of weight at different ages has 
been given in Chapter VII (page 196). A child who has become 
somewhat emaciated, either through rapid growth * or other 
causes, should have a larger food allowance than would ordinarily 
be required either for his age or for his weight. 

In calculating the food requirements of a family it is best 
not to estimate the needs of other members in terms of that of 
the man of the family (because men on account of the great 
differences in activity of their occupations are Hkely to be more 
variable in their energy requirements than are children of any 
given age) but rather to estimate the Calories for each mem- 
ber of the family separately according to his or her own needs 
and then sum up the total. Not infrequently other members 
of the family may require more food than the man^ especially 
if he be of less than average size and engaged in sedentary or 
other light work. 

The Problem of a Standard for Protein 

In attempting to set a standard for the amount of protein in 
the dietary we find no such definite and satisfactory basis for 
judgment as in the case of total food (or fuel) value. There is 
no indication that any kind of work necessarily increases the 

* Large as are the appetites of growing children it is not uncommon for the 
"growth impulse" to outrun the food intake so that the child although always having 
had access to ample food may as the result of very rapid growth be brought into a 
condition somewhat resembling that of the young animals described in the preceding 
chapter (page 338) which become emaciated through "attempting to grow" on 
rations suiBcient only for maintenance, i.e. through the growth of some tissues at 
the expense of others. As Aron points out a child in this condition has an abnor- 
mally low percentage of fat and high percentage of water in his body content. 
Hence he needs extra food not only to increase his weight up to that which corre- 
sponds to his height, but also to restore the normal percentage of fat in the body 
weight which he already has. 



374 CHEMISTRY OF FOOD AND NUTRFriON 

expenditure of protein as muscular work increases the expendi- 
ture of fuel, and the body cannot store up protein to anything 
like the extent that it stores fuel in the form of fat ; the feeding 
of protein above what is required for maintenance increases 
only slightly the store of protein which the body carries. 

When one writer proposes an amount of protein but little 
above the minimum required for equilibrium, while another 
advocates a much larger amount, there is implied a diflerence 
of view regarding protein such as no longer exists with respect 
to the energy metabolism. The difference, it is true, is hardly 
so great as might appear from a casual examination of the pro- 
posed standards. It may perhaps be most fairly expressed 
in terms of the relation between protein and energy in the 
different standards. Protein would contribute, according to the 
standards of Voit, Playfair, and Gautier, about i6 per cent of 
the fuel value of the food; of Atwater, about 15 per cent; of 
Langworthy, 12 per cent; of Chittenden, 8^ per cent. 

It will be of interest to examine some of the arguments which 
have been advanced in favor of a high protein or of a low pro- 
tein diet. The following extracts, given in chronological order, 
are from writings of those who had given special study to the 
subject and chiefly from the literature of the first decade of this 
century, when Chittenden's investigation of the protein require- 
ment was a subject of active discussion. The time of pubhca- 
tion of these opinions must not be overlooked, since some of 
the phenomena then attributed to differences in protein intake 
might perhaps now be attributed, in part at least, to the ash 
constituents and vitamines of the food. 

Opinions regarding the Value of Liberal Protein Diet 

Liebig believed that fats and carbohydrates were burned in 
the body primarily to supply it with warmth, and that protein 
alone served as the source of muscular work and other forms of 
tissue activity. He therefore classed the non-nitrogenous as 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 375 

" respiratory " and the nitrogenous as " plastic " foodstuflfs, and 
treated the proteins as playing a " nobler " part in nutrition than 
can be taken by fat or carbohydrate. Although it was soon 
demonstrated that carbohydrates and fats as well as protein 
serve the body in the production of muscular energy, yet the 
influence of Liebig's teaching, and of the great attention given 
to protein in Voit's classical researches on nutrition, together 
with the fact that protein is the most prominent constituent of 
protoplasm, has resulted in a strong tendency to associate high 
protein feeding with increased stamina and muscular power. 

The reasoning of those who appreciated the results of more 
recent experimental work, and yet believed the general attitude 
of Liebig and Voit to have been largely sustained by experience, 
is well expressed by Von Noorden, who wrote in 1893 : * 

" When one considers that the dietary habits of peoples are 
the results of biological laws, it would seem that the action of 
these laws, extending through the thousands of years of existence 
of the species, would have resulted in the estabUshment of suit- 
able habits regarding the amounts of protein consumed. The 
data gathered by Voit may be taken as showing that this 
normal habit involves the consumption of about 105 grams of 
digestible protein f per day, a smaller protein consumption 
being usually associated with weak individuals or inactive 
peoples. While men can maintain equilibrium on less, still 
it can rightly be said that a liberal protein consumption makes 
for a full development of the man. A single individual may 
for years, or even decades, offend against this biological law 
unpunished. When, however, the small consumption of protein 
continues for generations, there results a weak race." 

Von Noorden, however, is careful to add : 

* Freely translated from the first edition of Von Noorden's Pathologic der Stoff- 
wechsel. 

t Corresponding to Voit's allowance of 118 grams of total protein when the food 
for the sake of economy, as contemplated by Voit, is taken somewhat largely from 
vegetable sources. 



376 CHEMISTRY OF FOOD ANT) NUTRITION 

" On ihc other hand, the importance of protein must not be 
overestimated. A diet is not necessarily good because the 
amount of protein is right ; it must have the proper proportions 
of the non-nitrogenous nutrients as well, since the protein is not 
to be depended upon for the necessary fuel value. Better 
somewhat less protein with a liberal amount of total food than 
more protein with insufficient fuel value; the latter brings a 
rapid loss of strength, the former can be endured very well, at 
least for a long time, and very Hkely throughout the life of the 
individual." 

Chittenden, in 1905, had reached exactly the opposite conclu- 
sion, — that the products of protein metabolism are a constant 
menace to the well-being of the body, and that any excess of 
protein over what the body actually needs is likely to be directly 
injurious, and at best puts an unnecessary and useless strain 
upon the liver and kidneys. Chittenden had satisfied himself 
by his numerous and long-continued experiments that both 
physical and mental stamina are promoted by decreasing the 
amount of protein in the food : " Greater freedom from fatigue, 
greater aptitude for work, greater freedom from minor ailments, 
have gradually become associated in the writer's mind with this 
lowered protein metabolism and general condition of physiologi- 
cal economy " . . . (Physiological Economy in Nutrition, pages 
51, 127). 

Hutchison, in 1906, concluded that the normal amount 
of protein in a diet furnishing 3000 Calories should be placed 
at about 75 grams. This allows some margin above the 
results of Chittenden's experiments and agrees with the rela- 
tion of protein to calories in mother's milk, which Hutchison 
regards as nature's hint as to the proper balance of nitroge- 
nous and non-nitrogenous food for the human species {Chemi- 
cal News, Vol. 94, page 104). 

Folin held that the argument for a high protein diet based 
on the fact that large amounts of protein are commonly eaten 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 377 

by those who can afford it can be equally well applied to the 
dietetic use of alcoholic beverages and is no more convincing 
in one case than in the other ; while on the other hand, study of 
protein metabolism has given rather strong evidence that the 
body has no need of such amounts as are commonly eaten. 
The loss of body nitrogen which occurs in the early periods of 
restricted protein feeding, and which was not determined nor 
specifically discussed by Chittenden, is treated by Folin as 
follows: " All the Hving protoplasm in the animal organism is 
suspended in a fluid very rich in protein, and on account of the 
habitual use of more nitrogenous food than the tissues can use 
as protein, the organism is ordinarily in possession of approxi- 
mately the maximum amount of reserve protein in solution that 
it can advantageously retain. When the supply of food protein 
is stopped, the excess of reserved protein inside the organism is 
still sufficient to cause a rather large destruction of protein 
during the first day or two of protein starvation, and after that 
the protein catabolism is very small, provided sufficient non- 
nitrogenous food is available. But even then, and for many 
days thereafter, the protoplasm of the tissues has still an 
abundant supply of dissolved protein, and the normal activity of 
such tissues as the muscles is not at all impaired or diminished. 
When 30 grams or 40 grams of nitrogen have been lost by an 
average-sized man during a week or more of abstinence from 
nitrogenous food (but with an abundance of carbohydrate and 
fat) the Hving muscle tissues are still well supplied with all the 
protein that they can use. . . . The continuous excessive 
use of protein may lead, however, to an accumulation of a larger 
amount of reserve protein than the organism can with advantage 
retain in its fluid media. It is entirely possible that the con- 
tinuous maintenance of such an unnecessarily large supply of 
unorganized reserve material may sooner or later weaken one, 
or another, or all, of the living tissues. At any rate, it seems 
scarcely conceivable that the human organism, having all the 



378 CHEMISTRY OF FOOD AND NUTRFFION 

time access to food, can gain in efficiency on account of such an 
excess of stored protein. The carrying of excessive quantities 
of fat is considered as an impediment, the carrying of exces- 
sive quantities of unorganized protein may be none the less so 
because more common and less strikingly apparent" {American 
Journal of Physiology, Vol. 13, pages 131-132, 136-137). 

Benedict argued that general experience in animal feeding 
favors the use of liberal quantities of protein, and that " while 
men may for some months reduce the proportion of protein in 
their diet very markedly and apparently suffer no deleterious 
consequences, yet, nevertheless, a permanent reduction of the 
protein beyond that found to be the normal amount for man is 
not without possible danger. The fact that a subject can so 
adjust an artificial diet as to obtain nitrogenous equilibrium with 
an excretion of nitrogen amounting to about 2 or 3 grams per 
day is no logical argument for the permanent reduction of the 
nitrogen in food for the period of a lifetime. . . . Dietary 
studies all over the world show that in those communities where 
productive power, enterprise, and civilization are at their high- 
est, man has instinctively and independently selected Uberal 
rather than small quantities of protein" {American Journal 
of Physiology, Vol. 16, page 409). 

A similar position was taken by Meltzer, who compared the ap- 
petite for a liberal surplus of protein with the liberal way in which 
the body is provided with organs and tissues for nearly all of its 
functions, and concludes that " valuable as the facts which Chit- 
tenden and his colaborer found may be, they do not make 
obvious their theory that the minimum supply is the optimum — 
the ideal. The bodily health and vigor which people with one 
kidney still enjoy does not make the possession of only one 
kidney an ideal condition. The finding that the accepted 
standard of protein diet can be reduced to one half can be com- 
pared with the finding that the inspired oxygen can be reduced 
to one half without affecting the health and comfort of the 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 379 

individual, but no one deduces from the latter fact that the 
breathing of air so rarefied would be the ideal. . . . The 
storing away of protein, like the storing away of glycogen and 
fat, for use in expected and unexpected exceptional conditions 
is exactly like the superabundance of tissues in an organ of an 
animal, or like an extra beam in the support of a building or a 
bridge — a factor of safety " {Science, Vol. 25, page 481). 

In view of the arguments of Benedict and of Meltzer, it is of 
especial interest that in his later book Chittenden says : " It is 
certainly just as plausible to assume that increase in the con- 
sumption of protein food follows in the footsteps of commercial 
and other forms of prosperity, as to argue that prosperity or 
mental and physical development are the result of an increased 
intake of protein food. Protein foods are usually costly and the 
ability of a community to indulge freely in this form of dietetic 
luxury depends in large measure upon its commercial pros- 
perity." Moreover, Chittenden contends that his allowance of 
60 grams of protein per day for a man of average size is a 
perfectly trustworthy figure, with a reasonable margin of 
safety; that "dietetic requirements, and standard dietaries, 
are not to be founded upon the so-called cravings of appetite, 
but upon reason and intelligence reenforced by definite knowl- 
edge of the real necessities of the bodily machinery" ; that " we 
must be ever mindful of the fact, so many times expressed, that 
protein does not undergo complete oxidation in the body to 
simple gaseous products like the non-nitrogenous foods, but 
that there is left behind a residue not so easily disposed of " ; 
and that " there are many suggestions of improvement in bodily 
health, of greater efficiency in working power, and of greater 
freedom from disease, in a system of dietetics which aims to meet 
the physiological needs of the body without undue waste of 
energy and unnecessary drain upon the functions of digestion, 
absorption, excretion, and metabolism in general ..." {The 
Nutrition of Man, pages 160, 164, 227, 269). 



380 CHEMISTRY OF FOOD AND NUTRITION 

Plainly the dietary habit of well-to-do people and the diet- 
ary standards which have been generally accepted in the past 
tend to be decidedly hberal with respect to protein, and to 
prescribe it in quantities which may be believed to be benefi- 
cial but certainly are not known to be necessary. It does not 
seem advisable, however, to adopt as a standard the lowest 
amount of protein to which the body can adjust itself, but 
rather to regard as the normal requirement an amount which 
will enable the body to maintain not only its equilibrium, 
but also some such reserve store of protein as we are accustomed 
to carry. An allowance of about 75 grams of protein per 
man per day, which is 50 per cent above the average estimate 
of actual requirement (page 220), seems fully adequate in view 
of our present knowledge. 

A reasonable surplus of protein, from suitable food materials, 
can hardly be injurious and may be advantageous. Whether 
such a surplus should be especially recommended or not is 
largely an economic question. Where little can be spent for 
food and there is danger that too little food may be eaten, 
it would be a mistake to use a surplus of protein which could 
economically be replaced by other food of greater fuel value. 
In such cases one must not be misled by the popular state- 
ment that " protein builds tissue " into supposing that a lib- 
eral amount of protein can keep the body strong in spite of a 
deficiency in the total food. This impression is still somewhat 
prevalent, but is certainly incorrect. 

The body is weakened through getting too little food, be- 
cause body material must then be burned for fuel. So long as 
the total food be deficient, the loss of body substance will 
continue, because not only the food protein, but body tissues 
as well, must be burned to meet the energy requirement. To 
strengthen the body through the diet we must increase, not the 
protein alone, but primarily the total calories. 

Strengthening or weakening of the body by feeding ordi- 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 381 

narily depends much more upon the sufficiency or insufficiency 
of the energy value of the total food than upon the amount of 
protein which it contains. 

Protein Standards for Children and for Family Dietaries 

Little can be said with confidence regarding the best amount 
of protein for children after the nursing period. In practice 
well-planned dietaries for children usually contain between 10 
and 15 per cent of the total energy in the form of protein. 
During the years of rapid growth a considerable fraction of 
the protein of the food is utilized in the synthesis of body pro- 
teins ; and since the amount of food protein required to form a 
gram of body protein is variable, depending upon the amino acid 
make-up of the former, it is evident that the kind of protein 
supplied becomes a matter of great importance. Here chemical 
and physiological laboratory evidence, clinical experience, and 
its e\'ident place in nature all indicate plainly the superiority 
of milk as source of supply of protein for growth, whether the 
case be that of the growing child after weaning or of the nursling 
fed through the mother. The recommendation that family 
dietaries should whenever possible include " a quart of milk 
a day for every child " was aimed primarily to insure an appro- 
priate protein supply. Needless to say, the milk also supphes 
important amounts of many other substances essential to growth. 

Since the energy requirement is greatly increased by muscular 
activity and the protein requirement is not, it is evident that in 
the metabolism of normal adults the energy and protein require- 
ments will not run parallel. The protein requirement of the 
healthy adult depends chiefly upon his size, while his energy 
requirement depends chiefly upon his activity. 

In childhood both the energy requirement and the protein 
requirement are high — often two to three times as high per 
unit of weight as for adults without muscular work. More- 
over the high protein and energy requirements of the child as 



382 CHEMISTRY OF FOOD AND NUTRITION 

compared with the man are found to run ai)proximately parallel 
and as shown in a previous chapter the same proportion of pro- 
tein in terms of the total energy which seems rational for the 
adult dietary suffices also for the food requirements of the child 
provided in the latter case the food is of appropriate kind. 

In most family groups the differences in age and size will 
constitute a more prominent factor than the differences in 
activity, and since the former affect energy and protein require- 
ments in about the same proportion, it becomes feasible and 
convenient to set the protein allowance for ordinary family 
groups in terms of a proportion of the total food value. To 
allow for varying conditions and for individual preferences 
as well as to provide a Uberal margin for safety it is customary 
to consider that from 10 to 15 per cent of the total calories may 
be in the form of protein. 

In cases where the nutritive requirements of growth, preg- 
nancy, or lactation are to be met, the kind of protein is perhaps 
as important as the amount. 

Standards for the Calcium, Phosphorus, and Iron Content of 

the Dietary 

Formerly dietary standards took no account of the ash 
constituents because it was assumed that dietaries furnishing 
sufficient energy and protein would always be adequate as 
regards the " inorganic " elements. As explained in previous 
chapters this assumption is not safe in the case of calcium, 
phosphorus, or iron. In the light of present knowledge ade- 
quate dietary standards must provide for these elements. The 
experimental evidence regarding the minimum requirements of 
the body for each of these elements has been reviewed in earlier 
chapters and there has been but brief discussion of the relation 
between minimum and optimum amounts. 

The evidence thus far available indicates an average minimum 
requirement for equilibrium, per man per day, of 0.45 gram 



DIETARY STANDARDS AND ECOxNOMIC USE OF FOOD 383 

calcium (0.63 gram CaO), 0.96 gram phosphorus (2.20 grams 
P2O5), and about o.oio gram (10 milligrams) of iron. 

To allow only these quantities in the daily food would corre- 
spond to an allowance of only 50 grams per man per day of protein. 

If the standard allowance be set 50 per cent above the indi- 
cated average minimum corresponding to an allowance of 75 
grams of protein we obtain 

Calcium, 0.68 gram (equivalent to 0.95 gram of calcium 

oxide, CaO)". 
Phosphorus, 1.44 grams (equivalent to 3.30 grams of P2O5). 
Iron, 0.015 gram (15 milligrams). 

If these be taken as proper allowances per man of 70 kilograms 
whose energy requirement averages 3000 Calories per day, 
then the corresponding allowances for other adults or for families 
containing children could also be stated as follows : 





For Adults 

PER Kilogram of 

Body Weight 


For Children (or 

Families Containing 

Chlldrex) per 

100 Calories 


Protein 

Phosphorus 

Calcium 

Iron 


1.07 grams 
0.0206 gram 
0.0097 gram 
0.00022 gram 


2.5 * grams 
0.048 gram 
0.023 gram 
0.0005 gram 





If it be desired to provide as Hberal a margin of safety here 
as in the case of a protein allowance of 100 grams per man per 
day, then the above figures must obviously be increased by one 
third. 

The Unidentified Essentials 

Of the unidentified fat-soluble and water-soluble substances 
essential to normal metaboHsm we have as yet no direct quanti- 
tative measures, either of the proportions in which they occur 
in food or are needed in nutrition. In view of their importance 
* In the case of the child this should be mainly milk protein. 



384 CHEMISTRY OF FOOD AND NUTRITION 

it is plain that they should not be ignored in the planning of 
dietaries, either of children or adults. McCoUum and Sim- 
monds have recently shown that a low intake of either " fat 
soluble A " or " water soluble B " not only retards or suspends 
the growth of young animals but is also distinctly detrimental 
to adults. A diet furnishing barely enough of these essentials 
to support slow growth of young regularly resulted in sub- 
normal vitaUty when fed to adults; but the symptoms were 
not always the same, e.g. some of the adults lost weight 
while others maintained weight but lost vitality. They state : 
" Our results indicate that there is no low plane of intake of 
either of these substances which can be said to maintain an 
animal without loss of vitality. When the minimal amount 
necessary for the prevention of loss of weight is approached, 
the life of the animal is jeopardized if the diet is persisted in." 
They also find that " the animal can tolerate being limited to 
a very low intake of either the dietary A or B much better with 
an otherwise excellent diet than when it is less well constituted," 
and also that " it is better to have a liberal supply of one 
and a minimal supply of the other of the A and B than the 
minimal allowance of both." The presence of sufficient quan- 
tities of these substances is insured by making prominent in 
the diet the types of foods rich in them. These are chiefly : 
milk and its products, eggs, vegetables, fruits, and the outer 
portions of the cereal grains — all foods which it is wise to 
make prominent in the diet for other reasons as well. It 
will be remembered that " fat soluble A " and " water soluble 
B " may or may not occur abundantly in the same articles of 
food. Milk, eggs, and green vegetables appear to be rich in 
both; butter in " fat soluble A " and whole grains in " water 
soluble B." Thus either milk or eggs alone, or both butter 
and whole grain products, would provide the two kinds of un- 
identified essentials. When both economy and efficiency are 
considered, it appears that milk and vegetables are especially 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 385 

worthy of a more prominent place in the diet than is commonly 
given them in present American practice. 

Limitations 0} Dietary Standards. — At the risk of repetition 
let it be clear that too much weight must not be attached to any 
of the so-called dietary standards, i.e. to any attempt to state 
the requisites of an adequate diet in terms of quantities of cer- 
tain nutrients. As Atwater sought strongly to emphasize, a 
dietary standard at best is " only an indication, not a rule." 
Some of those who have been most active in recent investiga- 
tion are most emphatic in warning against the expectation that 
dietary standards can be made to embrace all the quahties 
which a diet must have in order to be permanently adequate. 
Thus Hart, McCollum, Steenbock, and Humphrey in a very 
recent article * say : 

" With this recognition of all the normal factors for adequate 
nutrition there must not simultaneously arise a desire for a 
mathematical expression of these factors in feeding standards. 
It is doubtful if this can ever be done, at least for certain of them. 
For example, the r61e of the mineral nutrients is so varied, in- 
cluding such widely separate functions as construction and con- 
trol through antagonism, as to make it seem futile to attempt 
an expression of absolute requirements when natural foods, 
with their diversity of mineral content, are involved. Even 
the recognition of differences in the quality of proteins and their 
relation to nutrition will make it more diflficult to continue ex- 
pressing protein requirements in exact quantities than before 
the development of such knowledge; and what can be said of 
the quantitative requirements of fat soluble A and water sol- 
uble B and their supply in feeding materials? We need more 
effort placed on the accumulation of information on the phys- 
iological behavior of feeding stuffs than on the attempts to 
bring out new mathematical expressions of feeding standards." 

* Proceedings of the National Academy of Sciences, Vol. 3, page 374 (May, 
igi7). 

20 



386 CHEMISTRY OF FOOD AXD NUTRITION 

The Economic Use of Food 

True economy in the use of food must be physiological as well 
as pecuniary economy. The diet must supply amply all the 
requirements of nutrition (not merely the appetite nor the need 
for energy and protein) and this must be accomplished without 
the expenditure of too large a proportion of the income. The 
majority of famiUes in the United States have had in recent 
normal times incomes of less than $800 per year, of which not 
over 45 per cent can be spent for food if other living conditions 
are to be at all satisfactory. This implies an allowance of ap- 
proximately one dollar per day for food for the " normal " family 
of five,* or 20 cents per capita per day. 

If this be taken as approximating the average expenditure 
in normal years, f it would follow that the sum annually spent 
for food in the United States is in- the neighborhood of 
$7,000,000,000. From such statistical estimates of the value 
of the different food industries as the writer has been able to 
find it would appear that this is distributed somewhat as follows : 

Meats, poultry, fish, and 

shellfish about $2,800,000,000 — or about 40 per cent. 

Eggs about $400,000,000 — or about 6 per cent. 

Milk about $500,000,000 — or about 7 per cent. 

Cheese about $50,000,000 — or less than i per cent. 

Butter and other fats . about $500,000,000 — or about 7 per cent. 

Grain products . . . about $1,000,000,000 — or about 14 per cent. 

Sugar, molasses, etc. . about $500,000,000 — or about 7 per cent. 

Vegetables about $500,000,000 — or about 7 per cent. 

Fruits about $300,000,000 — or about 4 per cent. 

Nuts t about $50,000,000 — or less than I per cent. 

Miscellaneous, § by difference about 6 to 7 per cent. 

* If the family of five be reckoned as equivalent in food requirements to 3.7 
men, the amount here suggested as available for food would correspond to 27 cents 
"per man per day" or "per unit." 

t No attempt is made in this chapter to quote the fluctuations of prices under 
war conditions. The economic relationships here discussed will be found to be but 
little disturbed by a general raising or lowering of the level of prices. 

I This estimate doubtless includes considerable quantities of nuts not used as 
such for human food but pressed for oil and the residue fed to farm animals. 

§ Including beverages, condiments, and minor uncla-ssitied food materials. 



DIETARY STANDARDS AND ECONO^IIC USE OF FOOD 387 

Any such estimates as these can be no more than rough ap- 
proximations since they depend upon data which are by no means 
complete and accurate for the year in which gathered and are 
subject to fluctuation from year to year. It also appears im- 
possible to avoid arbitrary assumptions regarding the relations 
of wholesale and retail values. They are intended, therefore, 
only to indicate in the most general way the relative prominence 
of expenditure for the different types of food materials as judged 
from the statistics of the food industries. 

Another statistical estimate may be obtained from the data 
published by the U. S. Bureau of Labor Statistics, who report 
that of the total value of food consumed in 2567 workingmen's 
families the distribution of expenditure was as follows : 



Per Cent of Total 
Cost of Food 



Meat, poultry, and fish . . . 

Eggs 

MUk 

Cheese 

Butterand lard 

Grain products 

Sugar and molasses . . . . 

Vegetables 

Fruit 

Other food and food adjuncts 



33-80 

S-H 
6.52 
0.80 
11.66 
9-57* 
S-34 
9.72 

505 

7-50 



These averages are based upon data which were apparently 
obtained, for the most part at least, by simply asking questions 
of the housewife regarding the kinds, amounts, and costs of her 
food purchases and relying upon her memory for the facts. 
The probable errors in data for individual families would thus 
be large, but the great number of families included in the inquiry 
would tend to minimize the errors in the final average. 

* Low partly because of purchase of flour rather than bread, partly because oat- 
meal, etc., were often not reported under this head but under "other foods." 



388 



CHEMISTRY OF FOOD AND NUTRITION 



A different kind of data bearing on this same problem is found 
in the dietary studies made under the auspices of the United 
States Department of Agriculture or of the New York Associa- 
tion for Improving the Condition of the Poor. These dietary 
studies are accurate records of the kinds and amounts of foods 
consumed by given groups of people during a period of a week 
or more. From such studies, chiefly of family groups, 208 
have been taken as presumably representative of American 
food habits generally, and the cost of these dietaries has been 
studied with reference to the distribution of expenditure under 
headings corresponding to those used in the case of the above 
statistical estimates with the following results: 



Per Cent of 

Total Cost 

OF Food 



Meats and fish (including poultr>' and shellfish if used) 

Eggs 

MUk (including cream if used) 

Cheese 

Butter and other fats 

Grain products 

Sugar, molasses, etc 

Vegetables 

Fruit (and nuts if used) 

Miscellaneous * 



34-3 
5-7 
9.6 
i.o 
8.6 

17-4 
4-5 

lO.I 

3-8 



Of the dietaries included in the above average, 92 constituted 
a series observed during 1914-1915 in connection with the food 
investigations of the New York Association for Improving the 
Condition of the Poor. These studies were not entirely confined 
to New York City nor to families of low incomes. The cost 
of food per man per day ranged from 12 to 76, averaging 34 
cents. The median cost was 31.5 cents per man per day. In 

* Tea, coffee, and other food adjuncts were usually but not always reported under 
this heading. The reported average is therefore somewhat below the truth. 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 389 

one fourth of the famiUes the cost was below 25 cents; in one 
fourth it was above 40 cents ; in one half it was between 25 and 
40 cents per man per day. 

The average distribution of expenditure in these 92 famihes 
was as follows : 



Per Cent of 

Total Cost 

OF Food 



Meat and fish (including poultry and shellfish when 
used) 

Eggs 

MUk (and cream if used) 

Cheese 

Butter and other fats 

Grain products 

Sugar, molasses, etc 

Vegetables 

Fruit 

Nuts 

Miscellaneous (chiefly beverages, condiments, and 
other food adjuncts) 



33-19 
5-55 
9.08 

I-I3 
8.14 

17.85 
3-8o 
9.12 
6.03 
0-35 

5.76 



When these 92 studies were grouped according to the amount 
spent per man per day for food, it was apparent that as the scale 
of expenditure became more liberal a larger proportion of the 
money was spent for butter and fruit and a smaller proportion 
for breadstuffs. The distribution of expenditure among other 
types of food was, however, very similar in the dietaries of low, 
medium, and high cost. 

Each of the three kinds of evidence used in arriving at the 
above estimates of distribution of expenditure for food may 
readily be criticized as inaccurate or inconclusive or both. Yet 
the trend of the data derived from the different kinds of evi- 
dence is so consistent that it can hardly be devoid of signifi- 
cance. It can scarcely be doubted that of the money devoted 
to the purchase of food the average American family spends 



390 CHEMISTRY OF FOOD AND NUTRITION 

from 30 to 40 per cent for meats and fish (including poultry 
and shellfish when used), about 5 or 6 per cent for eggs, about 
7 to 10 per cent for milk, from 7 to 12 per cent for butter and 
other fats, from 10 to 20 per cent for bread and other cereal 
and bakery products, 3 to 7 per cent for sugar and other sweets, 
7 to 10 per cent for vegetables, 2 to 8 per cent for fruit, and less 
than 2 per cent for cheese and nuts. At the same time it is 
plain that such a food budget, however prevalent, need not be 
regarded as fixed. Many people occasionally, and some habit- 
ually, put the last and smallest of the items just mentioned in 
the place of the first and largest by using cheese or nuts as so- 
called " meat substitute," more properly as an alternative to 
meat, — a custom which on the whole appears to be growing. 
The place of each type of food in the diet has been discussed 
in a general way elsewhere * and space does not permit us to 
go over the same ground here. 

That the writer does not regard the usual distribution of 
expenditure for food in American famiHes as being either inevi- 
table or ideal may be indicated by the fact that in his own house- 
hold, consisting of three adults and four growing children, the 
distribution of money expended for food is about as follows : 



Per Cent of 

Total Cost 

OF Food 



Meats, poultry, and fish 

Eggs 

Milk 

Cheese 

Butter and other fats 

Bread, cereals, and other grain products 
Sugar, molasses, and syrups .... 
Vegetables and fruits 



10-15 
5-7 

25-30 
2-3 

10-12 

12-15 
about 3 

1S-18 



* Sherman, Food Products, pages 74-81, io8-iii, 139-141, 212-216, 288-295, 
346-351. 357, 388-393, 440-444- 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 39 1 

Just what prominence should be given to each type of food 
in the provisioning of a given family or community is a problem 
calling for consideration of many factors. One important fea- 
ture of the problem is to ascertain how the normal distribution 
of expenditure among the various types of food materials affects 
the relative proportions of nutrients in the resulting mixed diet. 
The accompanying table permits a comparison between the 
expenditures for the different types of food and the returns 
from each in terms of energy, protein, calcium, phosphorus, and 
iron in the case of the series of 92 family dietaries described on 
page 389. In individual dietaries the returns will naturally 
vary according as an economical or an expensive food of its kind 
is chosen, but in the average of 92 different dietaries, each of a 
week's duration, the danger of error due to such individual 
variations is minimized. 



Each Type of Food in Percentage of Total (Average of 92 Dietaries) 



Meats and fish . . 
Eggs ..... 
Milk* . . . . 
Cheese .... 
Butter and other 

fats 

Grain products 
Sugar and molasses 
Vegetables . . . 

Fruits 

Nuts 

Miscellaneous . . 



Cost Calories Protein Calcium Phosphorus Iron 



33-19 
5-55 
9.08 

I-I3 

8.14 
17.85 
3.80 
9.12 
6.03 

0-3S 
5-76 



16.54 
1-75 
8.11 
0.94 

10.29 

37-79 
10.78 

9-03 
3-87 
0.27 
0.65 



36.29 

4-49 

10.13 

2.08 

0.28 
35-86 
0.07 
8.91 
1.08 
0.22 
0-59 



3-68 

3-25 
50.19 

7.28 

0.67 

15-31 
0.69 

13-25 
4.66 
0.14 



26.70 
4.00 

18.52 
2.96 

0.33 
28.85 
0.06 
14.65 
2.41 
0.26 
1.26 



31-43 
6.18 
4.72 
0-5S 

0.39 

24-95 
0.20 

26.22 
4.09 
0.18 
1.09 



If we compare the cost of each type of food with the energy and individual 
nutrients which it furnishes, we find that because of the differing prominence 
of the several factors of food value in the various types of food it is often 
difficult to decide which expenditures were more economical. Thus in the 
averages just given meat and fish cost one third of the total expenditure 

* Cream, in those cases in which it was purchased, is here included with milk. 
The amount of cream was small, if any. 



392 



CHEMISTRY OF FOOD AND NUTRITION 



for food and furnished about one third of the protein, phosphorus, and iron 
but only one sixth of the energy and only about one thirtieth of the calcium. 
Eggs furnished protein, phosphorus, and iron about in proportion to their 
cost, but less calcium and much less than a proportionate amount of energy. 
Milk furnished calories and protein about in proportion to cost, twice as 
much phosphorus, and fu'e times as much calcium in proportion, but only 
half as much iron. 

By adopting the principle of a score card and assigning weights to the 
different factors of food value, it becomes feasible to compute a "com- 
posite valuation" or "score" for each food or group of foods which may 
then be compared with its cost. Since the most frequent deficiency in 
American dietaries is inadequacy of total food or energy value and most 
dietaries actually observ^ed are of such composition as would furnish enough 
of each essential element if the total amount of food eaten were sufficient 
to provide a liberal energy supply, it seems reasonable to assign to the energy 
value of a diet a weight of about half of its composite valuation. It also 
seems reasonable to assign the remaining "points" equally to protein, 
calcium, phosphorus, and iron.* 

If then we giv^e to energy a weight of 60 on a scale of 100 and to protein, 
calcium, phosphorus, and iron each a weight of 10, or to energy 40 and to 
protein, calcium, phosphorus, and iron each 15, we obtain from the data 
of the table above the "score values" or "composite valuations" under 
the designations "I" and "II" respectively in the table which follows : 



Meats and fish 

Eggs 

Milk (and cream) 
Cheese . . . . - 
Butter and other fats 
Grain products 
Sugar and molasses 
Vegetables ... 

Fruit 

Nuts 

Miscellaneous . . 




* In reality this amounts to giving a higher valuation to the protein since this 
is counted both as protein and as a part of the energy supply as well. 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 393 

By comparing the composite valuation with the cost it will be seen that 
if either of these methods of estimating comparative values is at all valid, 
the mone)^ spent in these q2 families for milk and cheese, grain products, 
and vegetables brought a better relative return in food value and was there- 
fore in this sense better invested than the money spent for meats and fish, 
eggs, and fruit. 

In making any such comparison it must be kept prominently in mind : 
(i) that the weights assigned to the different factors of food value must 
necessarily be more or less arbitrarily chosen so that the resulting "com- 
posite valuations" or "food values" rest partly on facts and partly on 
assumptions; (2) that not all the important factors of food value are taken 
into account in these valuations, "vitamine values" for instance being 
wholly omitted from the calculation because as yet we have not the data 
necessary to permit us to give them numerical expression. It is quite 
possible that when it becomes feasible to state the vitamine values in numer- 
ical terms and give them due weight in the composite valuation, the expendi- 
tures for eggs and butter may appear more economical than is indicated 
by the above table. Any comparisons based on the use of such arbitrary 
weights or valuations as can at present be assigned must therefore be used 
with much discretion if misconceptions are to be avoided ; but if so used 
they may be found serviceable in guiding the economical choice of food and 
to some extent in teaching relative food values. 

Individual articles of food may be given " score values " or " composite 
valuations " in a similar manner. Thus if 100 Calories be given a value of 
40 on the scale of 100, and such quantities of protein, phosphorus, calcium 
and iron as should accompany 100 Calories in an adequate economical diet 
be given a value of 15 each, the score for almonds might be ascertained 
as follows : 

To every 100 Calories of almonds there are 3.23 grams of protein, 0.071 
gram of phosphorus, 0.039 gram of calcium, and 0.0006 gram of iron. If 
we accept the allowance* of 75 grams of protein, 1.44 grams of phosphorus, 
0.68 gram of calcium, and 15 milligrams of iron per man per day, then to 
every 100 Calories of the 3000 ordinarily taken as the requirement of a man 
at ordinary labor, there should be 2.5 grams of protein, 0.048 gram of phos- 
phorus, 0.023 gram of calcium, and 0.0005 gram of iron. Then to every 100 
Calories of almonds there is 1.3 (3.23 divided by 2.5) times the amount of 
protein required to " balance " the energy value ; 1.48 times the amount of 
phosphorus, 1.61 times the amount of calcium, and 1.2 times the amount of 
iron. Scoring these as indicated above, we have the score value for almonds 
as follows : 

* Sec page 383. 



394 



CHEMISTRY OF FOOD AND NUTRITION 



Assumed Values 



Calories (looj 40 

Protein i-3 X 15 

Phosphorus 1.48 X 15 

Calcium i. 61 X 15 

Iron 1.20 X 15 



Score 
Points 



40 

19-5 
22.2 
24.2 
18.0 
123.9 



Since a pound of almonds contains 16.14 loo-Calorie portions, then a 
pound of almonds has a score value of 2000 (123.9 multiplied by 16.14). 
The following table gives the score value of common typical foods : 

Approximate Score Valxje (Composite Valuation) per Pouxd of 
Some Common Typical Foods as Purchased 



Meat — Beef, sirloin 

Bacon 

Eggs 

Cheese — 

Cottage . . . . 

Hard American . . 
Milk — Condensed 
sweetened . . . 
unsweetened . . 

Skimmed . . . . 

Whole 

Butter 

Cream — 18.5% fat . 

40% fat . . . . 

Lard 

Olive oil 

Sugar 

Grain Products — . . 

Bread, entire wheat 

Bread, white 



1290 
1770 
1092 

1287 
4460 

2000 

1556 

500 

600 

2320 

860 

1350 

2450 

2450 

1090 

1250 
1098 



II* 



1460 
1460 
1341 

1688 
5690 

2200 

1955 
670 
700 

1750 
860 
1150 
1650 
1650 
725 

1320 
1060 



Grain Products (Con 

Bread, rye . 

Corn meal . 

Crackers . 

Corn flakes 

Farina . 

Flour, graham 

Flour, rye . 

Flour, white 

Hominy 

Macaroni . 

Oatmeal 

Rice, white 
Vegetables — 

Asparagus, fresh 

Beans, dry, white 

Beans, dry, Limas 

Beans, fresh Limas 

Beans, string . 

Beets .... 



1125 
1444 

1579 
1270 
1418 
2000 
1502 
1372 
1301 
1502 

2245 
1289 

279 
2750 
2380 
3(>3 
374 
246 



II* 



nil 

1360 

1433 
1090 
1308 
2150 
1459 
1257 
1147 
1444 
2465 
1 139 

368 

3350 

2780 

420 

472 

286 



*The two sets of arbitrary score values correspond to the two systems of 
"weights" or "points" explained above. The score value will vary slightly with 
the data of the particular analysis and should perhaps be expressed only in round 
numbers, 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 395 



Approximate Score Value (Composite Valuation) per Pound of 
Some Common Typical Foods as Purchased — Continued 



I* 


II* 


285 


367 


278 


338 


487 


640 


256 


350 


497 


523 


125 


153 


2834 


3464 


280 


380 


280 


330 


2510 


2960 


400 


475 


349 


405 


399 


374 


377 


414 


161 


195 


630 


890 


130 


144 


162 


192 


246 


307 


175 


156 


1075 


955 



II* 



Vegetables {Con) 

Cabbage . 

Carrots 

Cauliflower 

Celery . . 

Corn, canned 

Cucumbers 

Lentils . 

Lettuce . 

Onions . 

Peas, dry 

Peas, fresh 

Parsnips 

Potatoes, sweet 

Potatoes, white 

Radishes 

Spinach . 

Squash . 

Tomatoes 

Turnips 
Fruit — 

Apples, fresh 

Apples, dry 



Fruit {Con.) 

Bananas . 

Dates 

Grapefruit . 

Grapes . 

Lemons . 

Olives 

Oranges . 

Peaches, fresh 

Pears . . 

Pineapple 

Plums . . 

Prunes 

Raisins . 
Nuts — 

Almonds* 

Cocoa 

Filberts* 

Peanuts* 

Pecans* . 

Walnuts* 



254 

1298 

167 

286 

199 

1000 

209 

169 

236 

234 

345 

1 144 

1500 

1900 
2900 
1676 
2010 
1556 
730 



236 

1240 

169 

266 

228 

1000 

228 

177 

228 

253 

337 

"35 

1550 

2000 
3231 
1752 
2078 
1440 
670 



By dividing the " Score Value " of a pound of any food by the price in 
cents per pound one finds the number of score units or points of food value 
obtained for each cent, and a comparison of different foods on this basis 
gives some indication of their relative economy, if the limitations of such 
comparisons are held strictly in mind. Among these limitations may be 
mentioned (i) the fact already noted that such valuations necessarily in- 
volve the arbitrary assignment of weights to the different factors or phases 
of food value so that facts and assumptions are inseparably combined in 
the final results notwithstanding the numerical form in which these are 
expressed; (2) the further tacit assumption that a given amount of protein, 
of phosphorus, of calcium, or of iron is of th3 same value in whatever food 



* With sh^l. 



396 CHEMISTRY OF FOOD AND NUTRITION 

found, wliich is certainly not true in detail and may be very far from true 
in many cases ; (3) that any such attempt to reduce the values of different 
types of food to a single basis for comparison necessarily tends to obscure 
those differences of composition and character between the different types 
of food, which must be kept in mind in order that one may give each type 
of food its proper place and thus secure a well-balanced dietary. 

Let us return then to the consideration of the average data 
of the 92 dietaries as given in the table on page 391. 

The average food value of these 92 dietaries calculated per 
man per day was as follows : 

Energy 2928 Calories 

Protein loi Grams 

Calcium 0.72 Gram (i. 01 Grams CaO) 

Phosphorus 1.52 Grams (3.48 Grams P2O5) 

Iron 0.0166 Gram 

Comparing these averages with the amounts actually required 
for normal nutrition (page 383) it will be seen that the freely 
chosen dietaries contained a liberal surplus of protein and a fair 
supply of phosphorus and iron but scarcely more than is ac- 
tually necessary of calories or of calcium. Correspondingly we 
find that the number of individual family dietaries actually 
deficient in calcium and in total food value (calories) is high 
enough to cause serious concern, while the cases of deficiency 
of phosphorus or iron were considerably less frequent and there 
were few if any cases showing an actual deficiency of protein. 

Tfhis suggests that there would be true economy in a some- 
what different distribution of expenditure by which less should 
be spent for expensive high protein food, unless it is also rich 
in calcium or furnishes a high energy value in proportion to its 
cost, while more prominence should be given to those foods 
which are rich in calcium or are advantageous sources of energy 
without being conspicuously poor in phosphorus and iron. In 
general this would mean somewhat less meat and somewhat 
more of milk and vegetables, of the cheaper sorts of fruit, and 
of bread or other grain products in the diet. 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 397 

Breadstuffs and other staple grain products always give a high 
energy return as compared with their cost, and usually also a 
high return in protein and ash constituents, the latter, however, 
depending largely upon whether " whole grain " or highly 
milled products are used. In general the more economical 
the dietary must be the higher should be the proportion of ex- 
penditure for bread (or other grain products) and the more 
restricted the dietary the more desirable it becomes to use 
" whole grain " rather than highly milled products. 

Meats give usually, as compared with their cost, a fair return 
in protein, phosphorus, and iron, a low return in energy, and 
an extremely low return in calcium. Milk, on the other hand, is 
very rich in calcium and furnishes in proportion to its cost more 
energy and phosphorus than does meat of average fatness, and 
proteins and iron of at least equal value if not of equal amount. 
Milk also excels other foods in respect to the advantageous 
quantitative relationships of its ash constituents and is probably 
the best possible source of the growth-promoting substances 
needed by all young mammals. The well-known dietary rule of 
" a quart of milk a day for every child," already amply justified 
by practical results, has received additional support from several 
angles through the recent advances in our knowledge of the 
chemistry of nutrition. 

Armsby estimates that of the energy value of grain about 
18 per cent is recovered for human consumption in milk and 
only about 3.5 per cent in beef. 

While milk is somewhat poor in iron, that which it contains 
is exceptionally efficient in nutrition. Moreover, the supply 
of this element may readily be safeguarded either by the use of 
whole grain products or by increasing the proportion of fruits and 
vegetables in the diet. It will be recalled from what has been 
said in earlier chapters that an abundance of fruits and vege- 
tables in the diet is also advantageous in other important ways. 
Vegetables and some fruits, economically selected, bring a good 



398 CHEMISTRY OF FOOD AXD NUTRITION 

return in nutrients for the money expended and their liberal 
use adds greatly to both the attractiveness and the wholesome- 
ness of the diet. 

It therefore seems advisable to spend at least as much for 
fruit and vegetables as for meat and fish ; also to spend at least 
as much for milk as for meat (or for milk and cheese as for meat 
and fish). 

At ordinary prices eggs are about as cheap a food as meat, 
and cheese (like milk) is much cheaper than meat in proportion 
to its food value. Eggs and cheese can therefore be substi- 
tuted for meat to any extent desired in the individual dietary 
without detriment to its nutritive value and usually with good 
economy. 

General adoption of a dietary such as we now believe to be 
best would call for more milk and perhaps more vegetables and 
fruit than now come to our city markets; but more of these 
foods will be produced and marketed as the demand for them 
increases. Moreover an increased demand for these foods and 
a correspondingly decreased (per capita) demand for meat, so 
far from causing any serious " dislocation of industry," will 
help to facilitate natural evolution of American agriculture. 
With increasing population on stationary area farming neces- 
sarily becomes more intensive. Beef is produced less by the 
grazing of cattle on free ranges of unbroken prairie and more 
by the feeding of grain and other cultivated crops. For a given 
amount of food consumed a dairy herd yields a product of greater 
food value than does a herd of beef animals. An increasing 
ratio of milch cows to beef cattle is naturally to be expected 
with the development of a more intensive agriculture and will 
be to the advantage of producer and consumer alike. In re- 
gions adapted to dairy farming but too remote from large mar- 
kets to ship in the fresh state we may anticipate an increasing 
production of condensed and dried milk and of butter and cheese. 
An increased production of fruit and vegetables should also be 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 399 

a natural result of a more stable and intensive agriculture. At 
the same time the concentration of population in large cities 
increases the expense of transportation and makes the cost of 
retail distribution a serious item, especially in the case of bulky 
products with a relatively low value per pound. Cabbage, 
potatoes, and root crops can be produced at a low cost per ton, 
but the percentage of the cost of production which must be 
added when they are distributed through modern retail agencies 
tends constantly to increase. 

The more highly perishable fruits and vegetables having a 
higher cost per pound or ton are now successfully transported 
in transcontinental carload shipments. Precooling and low- 
ered temperatures in refrigerator cars, secured by the use of 
salt with ice, promise to reduce still further the losses incident 
to their transportation. 

Cold storage tends to equalize prices throughout the season 
on such perishable foods as butter, cheese, and eggs, and secures 
a supply of other fresh foods such as apples, of good quality, 
throughout almost the entire year. With the perfection of 
faciUties for more rapid distribution in cities after removal from 
freezing temperatures the number and quantity of vegetables 
and fruits so preserved should increase greatly. The canning 
industry has already developed to enormous proportions and 
it seems likely that drying processes will be applied to a con- 
stantly increasing number of the more bulky vegetables. 

The physical and economic wastes in marketing are being 
reduced by various agencies in the United States Department of 
Agriculture, now largely consoUdated in the Bureau of Markets, 
and in general the supply may be trusted to keep pace with the 
demand in the gradual shifting of emphasis from meat toward 
dairy products, vegetables, and fruit, which seems to be clearly 
desirable both in view of our present knowledge of nutrition, 
and in the light of our agricultural situation. 

The broader and more accurate conception of food values 



400 CHEMISTRY OF FOOD AND NUTRITION 

which is made possible by the recent advances in the chemistry 
of food and nutrition will guide the judgment both as to the 
proper emphasis to be placed upon each type of foods in the 
dietary and as to the wise selection among foods of the same 
type. It supplies the economic justification for the purchase 
of certain foods which would appear expensive if considered 
simply as sources of proteins, fats, and carbohydrates, and, on 
the other hand, it shows that some foods which are economical 
sources of protein and energy are also of high nutritive value in 
other respects. 

Making due allowance for all known factors which affect the 
nutritive value of foods, there remain large discrepancies be- 
tween nutritive value and market cost, and correspondingly 
ample opportunity for the exercise of true economy in the 
choice of food materials, 

REFERENCES 

Armsby. The Food Supply of the Future. Science, Vol. 30, page 817 
(1909). See also Ibid., Vol. 46, pages 160-162 (191 7). 

Atwater. Methods and Results of Investigation on the Chemistry and 
Economy of Food. Bull. 21, Ofiice of E.xpcrimcnt Stations, U. S. 
Dept. Agriculture (1895). 

Atwater. The Demands of the Body for Nourishment and Dietary Stand- 
ards. Fifteenth Report of the Storrs (Conn.) Agricultural E.xperi- 
ment Station, pages 123-146 (1903). 

Atwater. Neue Versuche ueber Stoff- und Kraftwechsel im menschlichcn 
Korper. Ergebnisse der Physiologie, Vol. 3,!, pages 497-604 (1904). 

Benedict. The Nutritive Requirements of the Body. American Journal 
of Physiology, Vol. 16, page 409 (1906). 

Chittenden. Physiological Economy in Nutrition (1905). 

Chittenden. The Nutrition of Man (1907). 

FoLiN. A Theory of Protein Metabolism. A mcrican Journal of Physiology, 
Vol. 13. page 117 (1905). 

Gephart AND LusK. Analysis and Cost of Ready to Serve Foods (Amer- 
ican Medical Association, Chicago). 

GiLLETT. Food Requirements of Children (Association for Improving 
the Condition of the Poor, New York). 



DIETARY STANDARDS AND ECONOMIC USE OF FOOD 401 

HiNDHEDE. Protein and Nutrition. 

Hutchison. Food and Dietetics. 

Kellogg and Taylor. The Food Problem. 

Langworthy. Food and Diet in the United States. Reprinted from the 
Yearbook of the U. S. Department of Agriculture for 1907. 

LusK. Science of Nutrition, Third Edition, Chapters 12 and 21. 

LusK. Food Economics. Journal of the Washiiiglon Academy of Sciences, 
Vol. 6, page 387 (June, 1916). 

LusK. Food Values. Science, Vol. 45, page 345 (April 13, 1917). 

McKay. The Protein Element in Nutrition. 

Meltzer. Factors of Safety in Animal Structure and Animal Economy. 
Harvey Society Lectures, 1906-1907, and Science, Vol. 25, page 481 
(1907). 

Mendel. Changes in the Food Supply and their Relation to Nutrition 
(Yale University Press). 

Sherman and Gillett. A Study of the Adequacy and Economy of Some 
City Dietaries (New York Association for Improving the Condition 
of the Poor). 

Taylor. The Diet of Prisoners of War in Germany. Journal of tlie Amer- 
ican Medical Association, Vol. 69, page 1575 (1917). 

U. S. Bureau of Labor Statistics (Bulletins and Reports). 

U. S. Census Bureau Reports. 

U. S. Department of Agriculture. Bureau of Markets (Bulletins, Cir- 
culars and Reports). 

U. S. Department of Agriculture, Office of Experiment Stations, Bulls. Nos. 
21, 29, 31, 38, 46, 52, 53, 55, 71, 75, 84, 91, 98, 107, 116, 129, 132, 149, 
150, 221, 223 (data and discussion of dietary studies). 

U. S. Department of Agriculture, Office of the Secretary. Reports 109, 
no, III, 112, 113. Meat Situation in the United States (1916). 

"The World's Food" (Papers by several authors). Annals of the American 
Academy of Political and Social Sciotce, Vol. 74, pages 1-293 (November, 
1917). 



APPENDICES 

APPENDIX A 

NOMENCLATURE AND CLASSIFICATION OF PROTEINS 

Joint Recommendations of the Committees on Protein Nomen- 
clature of the American Physiological Society and Ameri- 
can Society of Biological Chemists 

Since a chemical basis for the nomenclature of the proteins 
is at present not possible, it seemed important to recommend 
few changes in the names and definitions of generally accepted 
groups, even though, in many cases, these are not wholly satis- 
factory. The recommendations are as follows: 

First. — The word " proteid " should be abandoned. 

Second. — The word " protein " should designate that group 
of substances which consist, so far as at present is known, es- 
sentially of combinations of a-amino acids and their derivatives, 
e.g. oe-amino acetic acid or glycocoll ; a-amino propionic acid 
or alanine ; phenyl-ct-amino propionic acid or phenylalanine ; 
guanidin-a-amino valerianic acid or arginine, etc., and are 
therefore essentially polypeptids. 

Third. — That the following terms be used to designate the 
various groups of proteins : 

I. Simple Proteins. — Protein substances which yield only 
a-amino acids or their derivatives on hydrolysis. 

Although no means are at present available whereby the 
chemical individuality of any protein can be established, a 
number of simple proteins have been isolated from animal and 
vegetable tissues which have been so well characterized by 

403 



404 APPENDIX A 

constancy of ultimate composition and uniformity of physical 
properties that they may be treated as chemical individuals until 
further knowledge makes it possible to characterize them more 
definitely. 

The various groups of simple proteins may be designated as 
follows : 

(a) Alhumins. — Simple proteins soluble in pure water and 
coagulable by heat. 

{h) GlohuJins. — Simple proteins insolul)lc in pure water, but 
soluble in neutral solutions of salts of strong bases with strong 
acids.* 

(c) Glutelins. — Simple proteins insoluble in all neutral sol- 
vents but readily soluble in very dilute acids and alkalies. f 

(d) Alcohol-soluble Proteins. — Simple proteins soluble in 
relatively strong alcohol (70-80 per cent), but insoluble in water, 
absolute alcohol, and other neutral solvents. | 

(e) Albuminoids. — Simple proteins which possess essentially 
the same chemical structure as the other proteins, but are char- 
acterized by great insolubihty in all neutral solvents.§ 

(/) Histones. — Soluble in water and insoluble in very dilute 
ammonia, and, in the absence of ammonium salts, insoluble even 
in an excess of ammonia ; yield precipitates with solutions of 
other proteins and a coagulum on heating which is easily solu- 
ble in very dilute acids. On hydrolysis they yield a large 
number of amino acids, among which the basic ones predominate. 

(g) Protamins. — Simpler polypeptids than the proteins in- 

* The precipitation limits with ammonium sulphate should not be made a basis 
for distinguishing the albumins from the globulins. 

t Such substances occur in abundance in the seeds of cereals and doubtless rep- 
resent a well-defined group of simple proteins. 

% The subclasses defined (a, b, c, d) are exemplified by proteins obtained from 
both plants and animals. The use of appropriate prefixes will suffice to indicate 
the origin of the compounds, e.g. ovoglobulin, myoalbumin, etc. 

§ These form the principal organic constituents of the skeletal structure of ani- 
mals and also their external covering and its appendages. This definition does not 
provide for gelatin, which is, however, an artificial derivative of collagen. 



APPENDIX A 405 

eluded in the preceding groups. They are soluble in water, un- 
coagulable by heat, have the property of precipitating aqueous 
solutions of other proteins, possess strong basic properties, and 
form stable salts with strong mineral acids. They yield com- 
paratively few amino acids, among which the basic amino acids 
greatly predominate. 

II. Conjugated Proteins. — Substances which contain the 
protein molecule united to some other molecule or molecules 
otherwise than as a salt. 

(a) Nudcoprotcins. — Compounds of one or more protein 
molecules with nucleic acid. 

{h) Glycoproteins. — Compounds of the protein molecule 
with a substance or substances containing a carbohydrate 
group other than a nucleic acid. 

(c) P ho spho proteins. — Compounds of the protein molecule 
with some, as yet undefined, phosphorus-containing substance 
other than a nucleic acid or lecithin.* 

{d) Hemoglobins. — Compounds of the protein molecule 
with hematin or some similar substance. 

(e) Lecitho proteins, — Compounds of the protein molecule 
with lecithins (lecithans, phosphatids). 

III. Derived Proteins. 

I. Primary Protein Derivatives. — Derivatives of the protein 
molecule apparently formed through hydrolytic changes which 
involve only slight alterations of the protein molecule. 

(a) Proteans. — Insoluble products which apparently result 
from the incipient action of water, very dilute acids, or enzymes. 

{b) M eta proteins. — Products of the further action of acids 
and alkalies whereby the molecule is so far altered as to form 
products soluble in very weak acids and alkalies, but insoluble 
in neutral fluids. 

* The accumulated chemical evidence distinctly points to the propriety of 
classifying the phosphoproteins as conjugated compounds, i.e. they are possibly 
esters of some phosphoric acid or acids and protein. 



4o6 APPENDIX A 

This group will thus include ihc familiar " acid proteins " 
and " alkali proteins," not the salts of proteins with acids. 

(c) Coagulated Proteins. — Insoluble products which result 
from (i) the action of heat on their solutions, or (2) the action 
of alcohols on the protein. 

2. Secondary Protein Derivatives* — Products of the further 
hydrolytic cleavage of the protein molecule. 

(a) Proteoses. — Soluble in water, uncoagulated by heat, and 
precipitated by saturating their solutions with ammonium sul- 
phate or zinc sulphate. f 

(b) Peptones. — Soluble in water, uncoagulated by heat, but 
not precipitated by saturating their solutions with ammonium 
sulphate. J 

(c) Peptids. — Definitely characterized combinations of two 
or more amino acids, the carboxyl group of one being united 
with the amino group of the other, with the ehmination of a 
molecule of water.§ 

* The term " secondary hydrolytic derivatives " is used because the formation of 
the primary derivatives usually precedes the formation of these secondary- deriva- 
tives. 

t As thus defined, this term does not strictly cover all the protein derivatives 
commonly called proteoses, e.g. heterproteose and dysproteose. 

t In this group the kyrins may be included. For the present we believe that it 
will be helpful to retain this term as defined, reserving the expression "peptid" 
for the simpler compounds of definite structure, such as dipeptids, etc. 

§ The peptones are undoubtedly peptids or mixtures of peptids, the latter term 
being at present used to designate those of definite structure. 



APPENDIX B 
COMPOSITION OF FOODS 

Explanation of Headings 

Food as purchased may or may not consist entirely of edible 
material. When an article of food contains inedible matter or 
refuse, this may be stated separately and the composition of 
the edible portion then given, or the percentages of refuse and 
of edible nutrients in the original matter may be given so as to 
show directly the percentage of each edible nutrient obtained 
in the material as purchased. For example ; loo pounds of 
beef contains i6 pounds of bone and 84 pounds of moist flesh, 
of which 15.4 pounds are protein, 15 pounds fat, 53 pounds water, 
and 0.6 pound ash. The composition may be stated in either 
of the following forms : 

Composition of Beef 



Refuse 
Per Cent 


Water 
Per Cent 


Protein 
Per Cent 


Fat 
Per Cent 


Ash 
Per Cent 


16.0 


53-0 


15-4 


15.0 


0.6 





Composition of Beef 



Refuse. 


Edible Portion 


Per Cent 


Water 
Per Cent 


Protein 
Per Cent 


Fat 
Per Cent 


Ash 
Per Cent 


16.0 


63.1 


18.3 


17.9 


0.7 



407 



4o8 



APPENDIX B 



For most purposes it is convenient to include in one table 
the nutrients calculated both on the basis of edible material 
and of material as purchased. In such a case the percentage of 
refuse in the material as purchased may be given or may be 
omitted as in the following form : 

Composition of Beef 





Water 


Protein | Fat 

1 


Ash 


Edible portion (E. P.) 
As purchased (A. P.) 


63.1 
53-0 


18.3 
154 


17.9 
15.0 


0.7 
0.6 



In order to avoid confusion and possible errors in taking 
data from tables of composition it is important to note in 
which form the percentages are stated. Data given in either 
form are of course readily convertible into the other. In Table 
I which follows, the percentages of nutrients and the correspond- 
ing energy values are stated in the form last illustrated above. 
Table II shows percentages of ash constituents in the edible 
portion only. Table III shows grams of protein and of cal- 
cium, phosphorus, and iron in loo-Calorie portions, which esti- 
mates may obviously be used equally well whether the food be 
originally recorded in terms of edible material or of material as 
purchased. 

A word of explanation regarding the sources and reliability 
of the data may also be offered. The percentages of proteins, 
fats, and carbohydrates given in Table I are in the great ma- 
jority of cases taken from the tables of composition of American 
food materials compiled by Atwater and Bryant and published 
in Bulletin 28 of the Office of Experiment Stations, U. S. De- 
partment of Agriculture. By reference to this bulletin the reader 
may find the number of analyses on which the average is based 
and the maximum and minimum of the recorded percentages 
of each constituent, as well as the percentages of moisture, 



APPENDIX B 409 

ash, and in some cases crude fiber. The energy values given in 
Table I are computed from the average percentage of protein, 
fat, and carbohydrate by the use of the latest and most accurate 
factors (see page 143). The data for ash constituents given in 
Tables II and III are based on a critical compilation of all avail- 
able ash analyses, both American and European. In some cases 
only a single ash analysis could be found ; in other cases the 
data given are averages of many fairly concordant analyses. 
Between these extremes are data of all degrees of probable re- 
liability. It does not seem feasible to indicate the relative 
accuracy of the estimates for different articles of food. In 
general it may be said that only in the cases of the more impor- 
tant foods are the ash analyses as yet sufiiciently numerous 
and concordant to justify one in laying great emphasis upon 
comparisons of one article of food with another. More empha- 
sis can properly be laid upon estimates of the ash constituents 
of rations or dietaries made up of several food materials, since 
in such cases accidental errors will tend to offset each other. 
It is chiefly to facilitate such calculations that the tables have 
been made as complete as seemed practicable even though this 
necessitated including estimates of differing reliability on ap- 
parently equal terms. 

Data which are based in part at least upon assumptions are 
inclosed in parenthesis. They are not necessarily less accurate 
as estimates of average composition than are some of the di- 
rectly determined data of individual analyses. 

Since many unpublished ash analyses have been included in 
the present averages, Tables II and III will be found to present 
many differences in detail from those published elsewhere, or 
in the first edition of this book. The general trend of the aver- 
ages has, however, not been materially altered by the results 
of recent work. 

Attention may also be called to the fact that in Table II the 
data are uniformly given as percentages of the elements and 



4IO 



APPENDIX B 



not of their oxides. For the convenience of those who may 
prefer to continue to calculate calcium and phosphorus in terms 
of the oxides as has been customary in the past, Table III shows 
the weights of CaO and PjO;, as well as of protein, calcium, 
phosphorus, and iron in loo-Calorie portions of foods. 

TABLE I 

Edible Organic Nutrients and Fuel Values of Foods* 



Protein 
(NX6.2S) 

PER CENT 



Almonds E. P.f 

A. P.t 
Apples E. P. 

A. P. 
Apricots E. P. 

A. P. 
Artichoke, French . . . . E. P. 

A. P. 
Asparagus, fresh . . . . A. P. 

cooked A. P. 

Avocado E. P. 

A. P. 
Bacon, smoked E. P. 

A. P. 
Bananas E. P. 

A. P. 

Barley, pearled 

Beans, dried 

Lima, dried 

Lima, fresh E. P. 

A. P. 



2I.O 

"•5 
•4 
•3 
I.I 
i.o 
3-4 
1-7 
1.8 

2.1 
2.1 
1.4 

IO-5 

9-5 

1-3 

.8 

8.5 

22.5 

i8.i 
7-1 
3-2 



Fat 

PER 
CENT 



Carbo- 

j HY- 
DRATE 
PER 
CENT 



54-9 
30.2 

•5 
•3 



• 5 
•3 
.2 

3-3 
20.1 

13-2 

64.8 

59-4 
.6 

•4 
I.I 

1.8 
1-5 

•7 



•3 



17-3 

9-5 

14.2 

10.8 

13-4 

12.6 

12.0 

6.0 

3-3 
2.2 

7-4 
4.8 



22.0 
14-3 
77.8 
59-6 
65-9 
22.0 
9.9 



Fuel 
Value 

PER 

Pound 
Calo- 
ries 



100 
Calorie 
Portion 

GRAMS 



2940 
1615 

285 

214 

263 

247 

•300 

150 
100 

213 » 

993 

652 

2840 
2372 

447 

290 

1615 

i5<>5 
1586 

557 



15 

28 

159 
212 

174 
184 

151 
302 

450 
213 
46 
70 
16 
19 

lOI 

156 

28 

29 

29 

82 

182 



* The percentages of nutrients are taken from Bull. 28, Office of Experiment 
Stations, U. S. Department of .\griculture. The fuel values are calculated from 
these percentages by the use of the factors explained in Chapter V, viz. — protein, 
4 calories ; fat, g calories ; carbohydrate, 4 calories per gram. 

t E. P. signifies edible portion ; A. P. signifies as purchased. 



APPENDIX B 



411 



Table I — Continued 



Food 



Beans — Continued 
string, fresh E. P. 

A. P. 
baked, canned . . . . A. P. 
red kidney, canned . . . 
Beef, brisket, medium fat . E. P. 

A. P. 
chuck, average . . . . E. P. 

A. P. 
corned, average . . . . E. P. 

A. P. 
cross ribs, average . . . E. P. 

A. P. 
dried, salted, and smoked, E. P. 

A. P. 
flank, lean E. P. 

A. P. 
fore quarter, lean . . . E. P. 

A. P. 
fore shank, lean . . . . E. P. 

A. P. 
heart E. P. 

A. P. 
hind quarter, lean . . . E. P. 

A. P. 
hind shank, lean . . . E. P. 

A. P. 
hind shank, fat . . . . E. P. 

A. P. 
liver E. P. 

A. P. 
loin E. P. 

A. P. 
neck, lean E. P. 

A. P. 
neck, medium fat ... E. P. 

A. P. 



Protein 
(NX6.2S) 
per cent 


Fat 
per 

CENT 


Carbo- 
hy- 
drate 

PER 
CENT 


Fuel 
Value 

PER 

Pound 
Calo- 
ries 


100 
Calorie 
Portion 

GRAMS 


2-3 


•3 


7-4 


184 


241 


2.1 


•3 


6.9 


176 


259 


6.9 


2-5 


19.6 


583 


78 


7.0 


.2 


18.5 


471 


96 


15-8 


2S.5 


— 


1449 


31 


12.0 


22.3 


— 


1 130 


40 


19.2 


15-4 


— 


978 


46 


15-8 


12.5 


— 


797 


S8 


15-6 


26.2 


— 


1353 


34 


14-3 


23.8 


— 


1230 


37 


15-9 


28.2 


— 


1440 


32 


13-8 


24.8 


— 


1262 


36 


30-0 


6.5 


•4 


817 


56 


26.4 


6.9 


— 


760 


60 


20.8 


"•3 


— 


838 


54 


20.5 


II.O 


— 


821 


SS 


18.9 


12.2 


— 


842 


54 


14.7 


9-5 


— 


655 


69 


22.0 


6.1 


— 


647 


70 


14.0 


3-9 


— 


414 


no 


16.0 


20.4 


I.O 


1 140 


40 


14.8 


24.7 


•9 


1292 


35 


20.0 


13-4 


— 


907 


50 


16.7 


II. 2 


— 


757 


60 


21.9 


5-4 


— 


617 


75 


9.1 


2.2 


— 


255 


179 


20.4 


18.8 


— 


1171 


40 


9.9 


9.1 


— 


552 


83 


20.4 


4-5 


1-7 


584 


78 


20.2 


3-1 


2-5 


537 


85 


19.7 


12.7 


— 


877 


52 


17. 1 


II. I 


— 


764 


60 


21.4 


8.4 


— 


732 


62 


iS-i 


5-9 


— 


493 


93 


20.1 


16.5 


— 


1040 


44 


14.5 


II.O 


— 


740 


6t 



412 



APPENDIX B 



Table I — Continued 



Food 



PROTErN 

(NX6.25) 

PER CENT 



Beef — Continued 

plate, lean E. P. 

A. P. 
Porterhouse steak . . . E. P. 

A. P. 

rib rolls, lean A. P. 

ribs, lean E. P. 

A. P. 
ribs, fat E. P. 

A. P. 
round, lean E. P. 

A. P. 
round, free from visible fat 
rump, lean E. P. 

A. P. 
rump, fat E. P. 

A. P. 
sides, lean E. P. 

A. P. 
sirloin steak E. P. 

A. P. 

sweetbreads A. P. 

tenderloin A. P. 

tongue E. P. 

A. P. 

Beets, cooked E. P. 

fresh E. P. 

A. P. 

Blackberries A. P. 

Blackfish E. P. 

A. P. 
Bluefish E. P. 

A. P. 

Boston crackers 

Brazil nuts E. P. 

A. P. 



15.6 
13-0 
21.9 
19.1 
20.2 
19.6 

IS-2 
15.0 
12.7 
21.3 

19-5 
23.2 
20.9 
19.1 
16.8 
12.9 
19-3 
iS-S 
18.9 

16.S 
16.8 
16.2 
18.9 
14.1 

2.3 
1.6 

1-3 

1-3 

18.7 

7-4 

19.4 

10. o 

II.O 

17.0 
8.6 



Fat 

PER 
CENT 



Carbo- 
hy- 
drate 

PER 

cent 



18.8 

15-5 
20.4 
17.9 

IO-5 
12.0 

9-3 
35-6 
30.6 

7-9 

7-3 

2-5 

13-7 

II.O 

35-7 
27.6 
13.2 
10.6 
18.5 
16.1 
12. 1 
24.4 
9.2 
6.7 



i.o 
1-3 

■7 
1.2 

.6 

8.5 
66.8 

33-7 



7-4 

9-7 

7-7 

10.9 



3-5 



Fuel 
\'alue 100 

PER Calorie 
Pound | Portion 
Calo- I grams 

RIES 



IO5I 

867 

1230 

1077 

795 

84s 

654 

1721 

1480 

709 

649 

512 

940 

796 

1763 

1361 

890 

715 

1099 

960 

799 
1290 

717 
529 
180 
209 
167 
262 

393 
163 
402 
206 

1835 
3162 

1 591 



APPENDIX B 



413 



Table I — Continued 



Food 



Protein 


Fat 


(NX6.2S) 


PER 


PER CENT 


CENT 


6.0 


6.3 


8.9 


1.8 


9.0 


3-0 


"•5 


1.6 


9.1 


1.6 


9.6 


1.4 


9.4 


1.2 


9.2 


1-3 


0.7 


•9 


6.4 


1.2 


I.O 


85.0 


3-0 


•5 


27.9 


61.2 


3.8 


8.3 


1.6 


•3 


1.4 


.2 


4-3 


— 


I.I 


•4 


•9 


.2 


1.8 


•5 


I.I 


.1 


•9 


.1 


2.1 


2.8 


9.6 


I.I 


3-2 


.6 


28.8 


35-9 


29.6 


38.3 


27.7 


36.8 


20.9 


1.0 


259 


33-7 


15-9 


21.0 


18.7 


27.4 


29.9 


38.9 


22.6 


29-5 


27.6 


34-9 


1.0 


.8 


•9 


.8 



Carbo- 
hy- 
drate 

PER 
CENT 



Fuel 
Value 

per 
Pound 
Calo- 
ries 



100 
Calorie 
Portion 
grams 



Bread, Boston brown . . . 

graham 

rolls, water . . . . . 

toasted 

white, homemade . . . 

milk 

Vienna 

average white .... 

whole wheat 

Buckwheat flour .... 

Butter 

Buttermilk 

Butternuts E. P. 

A. P. 

Cabbage E. P. 

A. P. 

Calf's-foot jelly 

Carrots, fresh E. P. 

A. P. 

Cauliflower A. P. 

Celery E. P. 

A. P. 
Celery soup, canned . . . 

Cerealine 

Chard E. P 

Cheese, American pale . . 

American red .... 

Cheddar 

cottage 

full cream 

Fromage de Brie . . . 

NeufchS,tel 

pineapple 

roquefort 

Swiss 

Cherries, fresh E. P 

A. P 



S4-0 
52.1 
54-2 
61.2 

53-3 
5I-I 
54-1 
53-1 
49-7 
77-9 

4.8 
3-5 
•5 
5-6 
4.8 

174 
9-3 
7-4 
4-7 
3-3 
2.6 
5-0 

78.3 

S-O 

•3 

4.1 

4-3 

2.4 
1.4 

1-5 
2.6 
1.8 

1-3 

16.7 

15-9 



1345 
1 189 
1268 

1385 
1 199 
1158 
1 199 
1182 
1113 
1580 

3491 
162 

3065 
417 
143 
121 

394 
204 

158 

139 

84 

68 

243 
1640 

173 
1990 
2102 
2080 

499 
1890 
1 1 70 
1484 
2180 
1645 
1945 
354 
337 



34 
38 
36 
33 
38 
39 
38 
38 
41 
29 

13 

280 

IS 
109 

317 
376 

115 
221 
286 
328 
542 
672 
187 

28 
262 

23 



91 

24 
39 
31 
21 
28 

23 
128 

134 



414 



APPENDIX B 



Table I — Continued 



Food 



Protefn 
(NX6.2S) 

PER CENT 



Fat 

PER 
CENT 



Carbo- 
hy- 
drate 

PER 

CENT 



Fuel 

Value ioo 

PER Calorie 

Pound Portion 

Calo- crams 

RIES 



Cherries — Continued 

canned A. P. 

Chestnuts, fresh . . . . E. P. 

A. P. 

Chicken, broilers . . . . E. P. 

A. P. 

Chocolate 

Cocoa 

Cod, dressed A. P. 

salt E. P. 

A. P. 
Consomme, canned . . . A. P. 
Corn, green, canned . . . 

sweet, fresh E. P. 

A. P. 

Corn meal 

Cowpeas, dried 

green E. P. 

Crackers, butter . . . . A. P. 

cream A. P. 

graham A. P. 

soda . A. P. 

water A. P. 

Cranberries A. P. 

Cream 

Cucumbers E. P. 

A. P. 

Currants, fresh 

dried Zante 

Dandelion greens .... 

-Dates, dried E. P. 

A. P. 

Doughnuts 

Eggplant E. P. 

Eggs, uncooked E. P. 

A. P. 



I.I 

6.2 

5-2 
21-5 
12.8 

12.9 

21.6 

II. I 

254 

19.0 

2.5 

2.8 

3-1 
1.2 

9.2 

21.4 

9.4 

9.6 

9-7 

lO.O 

9.8 

10.7 

•4 

2.5 

.8 

• 7 

1-5 

2.4 

2.4 

2.1 

1.9 

6.7 

1.2 

13-4 
11.9 



5-4 

4-5 

2.5 

1-4 

48.7 

28.9 

.2 

•3 

•4 

1.2 
I.I 

•4 
1.9 
1.4 

.6 

lO.I 

12. 1 

9.4 

9.1 

8.8 

.6 

18.5 

.2 

.2 

1-7 
i.o 
2.8 

2-5 

21.0 

•3 

IO-5 

9-3 



21. 1 
42.1 
35-4 



30.3 
37-7 



•4 

19.0 

19.7 

7-7 

75-4 

60.8 

22.7 

71.6 

69.7 

73.8 

73-1 

71.9 

9.9 

4-5 

3-1 

2.6 

12.8 

74.2 

10.6 

78.4 
70.6 

53-1 
5-1 



407 

1098 

920 

493 

289 

2768 

2258 

209 

473 
361 

53 

455 

459 

178 

1620 

1550 

603 

1887 

1938 

1905 

1875 

1855 



79 
68 

259 

1455 

277 

1575 

1416 

1941 

126 

672 

594 



APPENDIX B 



415 



Table I — Continued 



Farina 

• Figs, dried 

Flounder A. P. 

E. P. 

Flour, r^'e 

wheat, California fine . . 

wheat, entire 

wheat, graham .... 
wheat, patent baker's grade 
wheat, straight grade . . 
wheat, average high and 

medium 

wheat, average low grade 

Fowls • E. P. 

A. P. 

Gelatin 

Grape butter 

Grapes E. P. 

A. P. 

Grapefruit E. P. 

A. P. 

Haddock E. P. 

A. P. 

Halibut steaks E. P. 

A. P. 

Ham, fresh, lean . . . . E. P. 

A. P. 

fresh, medium . . . . E. P. 

A. P. 

smoked, lean E. P. 

A. P. 

Herring, whole E. P. 

A. P. 

smoked E. P. 

A. P. 
Hominy 



Protein 
(NX6.2S) 

PER CENT 


Fat 

PER 
CENT 


Carbo- 
hy- 
drate 

PER 
CENT 


Fuel 
Value 

per 
Pound 
Calo- 
ries 


II. 


1.4 


76.3 


1640 


4-3 


•3 


74.2 


1437 


5-4 


■3 


— 


no 


14.2 


.6 


— 


282 


6.8 


•9 


78.7 


1590 


7-9 


1.4 


76.4 


1585 


13.8 


1.9 


71.9 


1630 


13-3 


2.2 


71.4 


1628 


13-3 


1-5 


72.7 


1623 


10.8 


I.I 


74.8 


1608 


11.4 


1.0 


75-1 


1610 


14.0 


1.9 


71.2 


1625 


19-3 


16.3 


— 


1017 


13-7 


12.3 


— 


752 


91.4 


.1 


— 


1660 


1.2 


.1 


58.5 


1088 


1-3 


1.6 


19.2 


437 


I.O 


1.2 


14.4 


328 


.6 


.1 


12.2 


235 


•4 


.1 


8.9 


172 


17.2 


•3 


— 


324 


8.4 


.2 


— 


160 


18.6 


5.2 


— 


550 


iS-3 


4.4 


— 


457 


25.0 


14.4 


— 


1042 


24.8 


14.2 


— 


1030 


15-3 


28.9 


— 


1458 


13-5 


25-9 


— 


1303 


19.8 


20.8 


— • 


1209 


17-5 


18.S 


— 


1073 


19.5 


7-1 


— 


644 


II. 2 


3-9 


— 


362 


36.9 


15-8 


— 


131S 


20.5 


8.8 


— 


731 


8.3 


.6 


790 


1609 



TOO 

Calorie 
Portion 
grams 



28 

32 

412 

161 

29 

29 
28 
28 
28 
28 

28 
28 

45 

60 

27 

42 

104 

138 

193 

264 

140 

283 

83 
100 

44 
44 
31 
35 
38 
42 
70 
125 
35 
62 
28 



4i6 



APPENDIX B 



Table I — Continued 



Food 



Protein 

(NX6.25) 

PER CENT 



Honey 

Huckleberries 

Kohl-rabi E. P. 

Koumiss ...... 

Lamb, breast E. P. 

A. P. 
chops, broiled . . . . E. P. 

fore quarter E. P. 

A. P. 

hind quarter E. P. 

A. P. 

leg, roast 

side E. P. 

A. P. 

Lard, refined 

Lemon juice 

Lemons E. P. 

A. P. 

Lettuce E. P. 

A. P. 

Liver, beef E. P. 

A. P. 

veal E. P. 

Lobster, whole E. P. 

A. P. 

canned A. P. 

Macaroni 

Macaroons 

Mackerel E. P. 

A. P. 

salt E. P. 

A. P. 
Marmalade, orange . . . 
Milk, condensed, sweetened 

skimmed 

whole 



•4 

.6 

2.0 

2.8 

19. 1 

iS-4 
21.7 

18.3 
14.9 
19.6 
16.S 
19.7 
17.6 
14.1 



i.o 

•7 
1.2 
1.0 
20.4 
20.2 
19.0 
16.4 

5-9 
18.1 

134 

6.5 

18.7 

10.2 

21. 1 

16.3 

.6 

8.8 

3-4 

3-3 



Fat 

PER 
CENT 



.6 
.1 
2.1 
23.6 
19.1 
29.9 
25.8 
21.0 
19.1 
16.1 
12.7 
23.1 
•18.7 

lOO.O 



•3 

.2 

4-5 
3-1 
5-3 
1.8 

• 7 
I.I 

•9 

15-2 

7-1 

4.2 

22.6 

17-4 
.1 

8.3 
•3 

J-.O 



Carbo- 
hy- 
drate 

PER 
CENT 



Fuel 

Value 100 

PER Calorie 

Pound Portion 

Calo- crams 

KIES 



8x.2 

16.6 

5-5 
5-4 



74- 
65- 



84-5 

54-1 

5-1 

=;.o 



1481 

140 

234 
1311 
1058 
1614 

1385 
1127 
1 149 

953 

876 

1263 

1015 

4080 

178 

201 

140 

87 
72 

583 

538 

562 

379 

139 

382 

1625 

1922 

629 

356 

1305 

1005 

1548 

1480 

167 

3T4 



APPENDIX B 



417 



Table I — Continued 



Food 



M'-" I , commercial 

homemade 

Molasses, cane 

Mushrooms V. P. 

Muskmelons E. P. 

A. P. 

Mutton, fore quarter . . . E. P. 

A. P. 

hind quarter E. P. 

V. P. 

leg E. P. 

A. P. 

side A. P. 

E. P. 

Nectarines I'L P. 

A. P. 

Oatmeal 

Okra E. P. 

A. P. 

Olives, green E. P. 

A. P. 

ripe E. P. 

A. P. 

Onions, fresh E. P. 

A. P. 

Oranges E. P. 

A. P. 
Oxtail soup, canned . . . A. P. 

Oysters E. P. 

in shell A. P. 

canned A. P. 

Parsnips E. P. 

A. P. 
Pea soup, canned .... A. P. 
Peaches, canned . . . . A. P. 

fresh E. P. 

A. P. 



Protein 
(NX6.25) 

PER CENT 


Fat 
per 

CENT 


Carbo- 
hy- 
drate 
per 

CENT 


Fuel 
Value 

PER 

Pound 
Calo- 
ries 


100 
Calorie 
Portion 
grams 


6.7 


1.4 


60.2 


1280 


36 


4.8 


6.7 


32.1 


942 


48 


2.4 





69-3 


1302 


35 


3-5 


•4 


6.8 


204 


223 


.6 


— 


9-3 


180 


252 


•3 


— 


4.6 


89 


5^0 


15.6 


30-9 


— 


1543 


29 


12.3 


24-5 


— 


1223 


37 


16.7 


28.1 


— 


1450 


31 


13-8 


23.2 


— 


1197 


38 


19.8 


12.4 


— 


863 


52 


16.5 


IO-3 


— 


718 


63 


I3-0 


24.0 


— 


1215 


37 


16.2 


29.8 


— 


1512 


30 


.6 


— 


15-9 


299 


152 


.6 


— 


14.8 


280 


162 


16.1 


7.2 


67.5 


1811 


25 


1.6 


.2 


7-4 


172 


264 


1.4 


.2 


6.5 


152 


300 


I.I 


27.6 


11.6 


1357 


33 


.8 


20.2 


8.5 


995 


46 


1-7 


25.0 


4-3 


1 130 


40 


1.4 


21.0 


3-5 


947 


48 


1.6 


•3 


9.9 


220 


206 


1.4 


•3 


8.9 


199 


228 


.8 


.2 


11.6 


233 


19s 


.6 


.1 


8.5 


169 


268 


3-8 


•5 


4.2 


166 


274 


6.2 


1.2 


3-7 


228 


199 


1.2 


.2 


• 7 


43 


1065 


8.8 


2.4 


3-9 


328 


138 


1.6 


•5 


13-5 


294 


154 


1-3 


•4 


10.8 


236 


192 


3.6 


• 7 


7.6 


232 


196 


• 7 


.1 


10.8 


213 


213 


• 7 


.1 


9.4 


188 


242 


•5 


.1 


7-7 


153 


297 



2E 



4i8 



APPENDIX B 



Table I — Continued 



Food 



Peanuts E. P. 

A. P. 

Pears, fresh E. P. 

A. P. 

Peas, canned A. P. 

dried 

green E. P. 

A. P. 

Peppers, green E. P. 

Persimmons E. P. 

Pies, apple 

custard 

lemon 

mince 

squash 

Pineapples, fresh . . . . E. P. 

canned A. P. 

Pine nuts (pignolias) . . . 
Pistachios, shelled .... 

Plums E. P. 

A. P. 

Pomegranates E. P. 

Pork, chops, medium . . . E. P. 

A. P. 

chuck ribs and shoulder . E. P. 

A. P. 

fat, salt A. P. 

sausage A. P. 

side E. P. 

A. P. 

tenderloin A. P. 

Potato chips A. P. 

Potatoes, white, raw . . . E. P. 
A. P. 

sweet, raw E. P. 

A. P. 



Protein 
(NX6.2S) 

PERCENT 


Fat 

PER 

CENT 


Carbo- 
hy- 
drate 

PER 
CENT 


Fuel 
Value 

PER 

Pound 
Calo- 
ries 


25.8 


38.6 


24.4 


2490 


19.5 


29.1 


18.5 


1877 


.6 


•5 


I4.I 


288 


•5 


■4 


12.7 


256 


3-6 


.2 


9.8 


252 


24.6 


1.0 


62.0 


161 1 


7.0 


•5 


16.9 


454 


3.6 


.2 


9.8 


252 


I.I 


.1 


4.6 


109 


.8 


•7 


31.5 


615 


3-1 


9.8 


42.8 


1233 


4.2 


6.3 


26.1 


806 


3-6 


lO.I 


37-4 


1156 


5-8 


12.3 


38.1 


1300 


4.4 


8.4 


21.7 


817 


■4 


•3 


9-7 


196 


•4 


• 7 


36.4 


695 


33-9 


49-4 


6.9 


2757 


22.3 


54-0 


16.3 


2900 


I.O 


— 


20.1 


383 


•9 


— 


19.1 


363 


1-5 


1.6 


19.5 


447 


16.6 


30.1 


— 


1530 


134 


24.2 


— 


1230 


17-3 


311 


— 


1585 


14.1 


25-5 


— 


1298 


1.9 


86.2 


— 


3555 


I3-0 


44.2 


I.I 


2030 


9.1 


55-3 


— 


2423 


8.0 


49.0 


— 


2145 


18.9 


130 


— 


875 


6.8 


39-8 


46.7 


2598 


2.2 


.1 


18.4 


378 


1.8 


.1 


14-7 


302 


1.8 


• 7 


27.4 


558 


1-4 


.6 


21.9 


447 



APPENDIX B 



419 



Table I — Continued 



Food 



Prunes, dried E. P. 

A. P, 
Pumpkins E. P. 

A. P. 
Radishes E. P. 

A. P. 
Raisins E. P. 

A. P. 
Raspberries, red .... 

black 

Rhubarb E. P. 

A. P. 

Rice 

Salmon, dressed A. P. 

whole E. P. 

A. P. 
Sausage, Bologna . . . . E. P. 

A. P. 
farmer E. P. 

A. P. 
Shad, whole E. P. 

A. P. 

roe 

Shredded wheat .... 

Spinach, fresh A. P. 

Squash E. P. 

A. P. 

Strawberries 

Succotash, canned .... 

Sugar 

Tomatoes, fresh A. P. 

canned A. P. 

Tuna (tunny fish) . . . . E. P. 
Turkey E. P. 

A. P. 
sandwich, canned . . . 



Protein 
(NX6.25) 
per cent 


Fat 
per 

CENT 


Carbo- 
hy- 
drate 

PER 
CENT 


Fuel 
Value 

per 
Pound 
Calo- 
ries 


2.1 





73-3 


1368 


1.8 


— 


62.2 


1160 


I.O 


.1 


5-2 


117 


•5 


.1 


2.6 


60 


1-3 


.1 


5-8 


133 


•9 


.1 


4.0 


91 


2.6 


3,-i 


76.1 


1562 


2-3 


3-0 


68.5 


1407 


1.0 


— 


12.6 


247 


1-7 


1.0 


12.6 


300 


.6 


■ 7 


3.6 


105 


•4 


•4 


2.2 


63 


8.0 


•3 


79.0 


1591 


13.8 


8.1 


— 


582 


22.0 


12.8 


— 


923 


15.3 


8.9 


— 


642 


18.7 


17.6 


•3 


1061 


18.2 


19.7 


— 


"35 


29.0 


42.0 


— 


2240 


27.9 


40.4 


— 


2156 


18.8 


9-5 


— 


727 


94 


4.8 


^ 


367 


20.9 


3.8 


2.6 


582 


10.5 


1-4 


77-9 


1660 


2.1 


•3 


3-2 


109 


1.4 


•5 


9.0 


209 


•7 


.2 


4-5 


103 


1.0 


.6 


7-4 


169 


3-6 


1.0 


18.6 


444 


— 


— 


1 00.0 


1815 


•9 


•4 


3-9 


104 


1.2 


.2 


4.0 


103 


26.6 


11.4 


— 


946 


21. 1 


22.9 


— 


1320 


16.1 


18.4 


— 


1042 


20.7 


29.2 


— 


1568 



100 
Calorie 
Portion 
grams 



2>Z 

39 

389 

753 

341 

488 

29 

32 

184 

151 

433 

714 

29 

78 

49 

71 

43 

40 

20 

21 

61 

124 

78 

27 

417 

217 

443 
269 
102 

25 
438 
443 

48 

34 
43 
29 



420 



APPENDIX B 



Table I — Continued 



Food 



'luiiiips E. P. 

A. P. 

Veal, breast E. P. 

A. P. 

cutlet E. P. 

A. P. 

fore quarter E. P. 

A. P. 

hind quarter E. P. 

A. P. 

side E. P. 

A. P. 
Vegetable soup, canned . . 
Walnuts, California or Eng- 
lish E. P. 

A. P. 

black E. P. 

A. P. 

Watermelons E. P. 

A. P. 

Wheat, cracked 

Whitefish E. P. 

A. P. 
Zwieback 



Protein 
(NX6.2S) 

PER CENT 


Fat 

PER 

cent 


Carbo- 

HV- 

DRAIE 

PER 

CENT 


Fuel 
Value 

per 
Pound 
Calo- 
ries 


1-3 


2 


8.1 


178 


■9 


.1 


5-7 


124 


20.3 


II.O 


— 


817 


15-3 


8.6 


— 


629 


20.3 


7.7 


— 


683 


20.1 


7-5 


— 


670 


20.0 


8.0 


— 


690 


15-1 


6.0 


— 


517 


20.7 


8.3 


— 


715 


16.2 


6.6 


— 


534 


20.2 


8.1 


— 


697 


15.6 


6.3 


— 


539 


2.9 


— 


•5 


62 


18.4 


64.4 


13-0 


3199 


4.9 


17-3 


3 


S 


859 


27.6 


56.3 


II 


7 


301 1 


7.2 


14.6 


3 





780 


•4 


.2 


6 


7 


136 


.2 


.1 


2 


7 


57 


II. I 


1-7 


75 


5 


1635 


22.9 


6.5 


— 


680 


10.6 


3-0 


— 


315 


9.8 


9.9 


73 


S 


1915 



TOO 

Calorie 
Portion 
grams 



256 
367 
56 
72 
66 
68 
66 
88 
64 
85 
65 
84 
735 

14 

53 

IS 

59 

332 

800 

28 

67 

144 

24 



APPENDIX B 



421 



TABLE II 

Ash Constituents of Foods in Percentage of the Edible Portion 
(Compiled from Various Sources) 



Food 



Almonds . . . . 
Apples . . . . 

dried . . . . 
Apricots . . . . 

dried . . . . 
Asparagus . . . 
Bacon (See Meat) 
Bananas . . . . 
Barley, entire . . 

pearled . . . 
Beans, dried . . 

kidney, dry . . 

Lima, dry . . 

Lima, fresh . . 
- string, fresh . . 
Beef (See Meat) 

Beer 

Beets 

Blackberries . . . 
Blood (avg.) . . 
Blueberries . . . 
Bluefish (See Fish) 
Bread, 

Boston brown 

"entire wheat" 

graham . . 

rye .... 

white . . . 
Breadfruit . . 
Brussels sprouts 
Buckwheat flour 
Butter . . . 
Buttermilk . . 



•239 
.007 
.032 
.014 
(.066) 
.025 



.009 

■043 
.020 
.160 
.132 
.071 
.028 
.046 

.004 
.029 
.017 
.008 
.020 



.129 
(.05) 
(•05) 
.024 
.027 
.084 
.027 
■039 
•015 
.105 



Wm 

zS 



•251 
.008 

•037 
.010 

(■047) 
.011 

.028 
.iji 

(.070) 
.156 
•139 
.188 

(.070) 
.025 

.008 
.021 
.021 
.004 
.007 



.078 
(.OS) 
(.05) 
■039 
.023 
.007 
.040 
.048 
.001 
.016 



ciUi 






.741 
.127 
(.623) 
.248 

(1-157) 
.196 

.401 

•477 
(.241) 
1.229 
1. 144 
1. 741 

(■613) 
.247 

.058 

•353 
.169 

■075 
•051 



(•232) 
(.208) 
(.291) 

•151 
.108 

•235 
•375 
.130 
.014 
•151 






.019 
.011 

(-050) 
.038 

(•177) 
.007 

•034 
.076 

(•037) 
.097 
.041 
.249 

(.088) 
.019 

.013 

•093 

(.007) 
.261 
.016 



(■394) 
(•394) 
(■394) 
.701 

(•394) 
.027 
.004 
.027 

(.788) 
.064 



r1 ^' 



•465 
.012 
.048 
.025 
(•117) 
•039 

.031 
.400 
.181 
.471 

•475 
•338 
• 133 
•052 

.028 
•039 
•034 
■031 
.008 



• 185 
(.175) 
(•218) 

.148 

•093 
.068 
.120 
.226 
.017 
.097 



•037 

.005 
(•025) 

.002 
(.009) 

•039 

.125 
.016 

(.016) 
.032 
.041 
.026 

(.009) 
.024 

.006 
.058 
(.010) 
.280 
.008 



(.607) 

(.607) 

(.607) 

1.025 

(•607) 

.100 

.040 

.012 

(1.212) 

.099 



.160 

.006 

? 

.010 

? 

.041 

.010 

•153 

(.120) 
.215 
.227 
.161 

(•057) 
.030 

•015 
.016 
.020 

• 137 
.011 



.201 
(.120) 
.150 
.104 
.105 
.049 
.194 
.071 
(.010) 
.026 



422 



APPENDIX B 



Table II — Continued 



Food 



Cabbage .... 
Cabbage greens 
Cantaloupe . . . 
Capers . . . . 
Carp (See Fish) 
Carrots .... 
Cauliflower . . . 
Caviar .... 
Celery .... 

Chard 

Cheese .... 
Cherries .... 
Cherry juice . . 
Chestnuts . . . 
Chicken (See Meat) 
Chocolate . . . 

Cider 

Citron . . . . 
Clams, round . . 

soft, long . . . 

Cocoa 

Coconut, dried . 

fresh .... 
Coconut milk . . 
Cod (See Fish) 
Corn(maize),mature 

meal . . . 

sweet . 

sweet, dried . 
Cotton-seed meal 
Cowpeas . 
Crackers . . . 
Cranberries . . 
Cream . . . 
Cucumbers . . 
Currants, dried 

fresh . . . 






•045 

.106 
.017 

.122 

.056 
.123 

•137 
.078 
■150 
•931 
.019 
.017 
•034 

.092 
.008 
.121 
.106 
.124 
.112 
•059 
.024 
.020 

.020 
.018 
.006 
.021 
.265 
.100 
.022 
.018 
.086 
.016 
.082 
.026 



< a 
SB 



•015 
.030 
.012 
.022 

.021 
.014 
.022 
.014 
.071 

•037 
.016 
.011 
•051 

(-293) 
.011 
.018 
.098 
.079 
.420 

•059 
.020 
.009 

.121 
.084 

•033 
.121 
.462 
.208 
.011 
.007 
.010 
.009 
.044 
.017 



si 

Oh B 



.247 

■512 

•235 
.209 

.287 

.222 
.422 
.316 
.318 
.089 

•213 
.200 
.560 

(-563) 
•095 
.210 

•131 
.212 
.900 

•597 
.300 
.144 

•339 
.213 

•113 
.414. 
1.390 
1.402 
.100 
.077 
.126 
.140 

.873 
.211 






.027 
.025 
.061 
•051 

.101 
.068 
.874 
.084 
.086 
.606 
.023 
.013 
.065 

.012 
.020 
.011 

•705 
.500 

•059 
•073 
.036 



.036 

•039 
.040 
.146 

•234 
.161 

(•594) 
.010 

■035 
.010 
.081 
.007 



^£ 



.029 
.099 

•015 
.062 

.046 
.061 
.176 

•037 
.040 
•683 

•031 
.018 

•093 

•455 
.009 

•033 
.046 
.122 
.709 

•155 
.074 
.010 

.283 

.190 

.103 

•376 

i^i93 

•456 

.102 

•013 

.067 

•033 

•195 

.038 



.024 
.068 
.041 



.036 
.050 
1.819 
.156 
•039 
.880 
.014 
.003 
.006 

(■051) 
.006 
•003 

1.220 
.910 
■051 
• 239 
.120 



■045 
.146 
.014 
.050 

•037 
.040 
(.910) 
.009 
.080 
•030 
.060 
.006 



.066 

■'^73 
.014 



.022 
.086 

.022 

.124. 
.263 
.Oil 
.006 
.068 



.006 
.020 
.224 

•213 
•203 
(■056) 
.028 
.008 

•151 
.III 
.046 
.167 

•485 
.240 
•125 
.007 
.030 
.020 
.044 
.014 






.0011 
.0018 
.0003 



.0006 
.0006 

.0005 
(.0025) 

.0013 

.0004 
(.0003) 

.0007 

(.0027) 
(.0002) 



.0027 



.0029 
.0009 
.0008 
.0029 



.0015 
.0006 
.00022 
.0002 
(■0025) 
.0005 



APPENDIX B 



423 



Table II — Continued 



Food 



Currant juice . . 
Dandelion . . . 

Dates 

Duck (See Meat) 
Eggplant .... 

Eggs 

Egg white . . . 
Egg yolk .... 
Endive . . . . 
Farina . . . . 
Figs, dried . . . 

fresh .... 
Fish* 

Flaxseed . . . . 
Flour, buckwheat . 

"entire wheat" . 

graham . . . 

white . . . . 



rye 

Fowl (See Meat) 
Gluten feed . . . 
Goose (See Meat) 
Gooseberries . . 
Grapefruit . . . 
Grapejuice . . . 
Grapes . . . . 
Guava . . . . 
Haddock (See Fish) 
Halibut (See Fish) 
Ham (See Meat) 
Hazelnuts . . . 
Herring (See Fish) 
Hominy .... 



.021 

• 105 
.065 

.011 
.067 
•015 

• 137 
.104 
.021 
.162 
•053 

.204 
.010 
.031 

•039 
.020 
.018 

.247 

•035 
.021 
.011 

.OIQ 
.014 



287 



SB 



.010 
.036 
.069 

•015 
.011 
.010 
.016 
.013 
.025 
.071 
.022 

.252 
.048 

(.090) 

(•133) 
.018 
.081 



.014 
.009 
.009 
.010 
.008 



.140 
.058 



.185 
.461 
.611 

(.140) 
.140 
.160 

• "5 
.380 
.120 
.964 
■303 

.901 
.130 

(•274) 
(.457) 

• 115 
•463 

.250 

.197 
.161 
.106 
.197 
•384 



.618 
.174 






(.006) 
.168 
•055 

(.010) 

■143 

.156 

.075 

.109 

.065 

.046 



.050 
.027 
(•037) 
(•037) 
.060 
.019 

.420 

.038 
.004 
•005 
•015 



.019 



.018 
.072 
.056 

•034 
.180 
.014 
•524 
.038 
•125 
.116 
.036 

.627 
.176 
.238 

•364 
.092 
.289 

•542 

.031 
.020 
.011 

■031 
.030 



•354 
.144 



2^ 



.004 
.099 

.228 

.024 
.106 

•155' 
.094 
.167 
.076 

•043 
.014 

.022 
.012 

(.070) 

(.070) 

.074 

•055 

.090 



.005 
.002 
.005 
■045 



.067 
.046 



.005 
.017 
.070 

.016 

•195 
.216 
.166 
•035 
•155 
.056 
.010 

.170 
.071 
(.180) 
.183 
.177 
.123 

.558 

.011 
.010 
.009 
.024 



(.136) 



* Average fish is estimated to contain per loo grams of protein as follows : 
o.iOQ gram Ca; 0.1.33 gram Mg; 1.671 grams K; 0.373 gram Na; 1.148 grams 
P; 0.528 gram CI; 1.119 grams S; 0.0055 gram Fe. 



424 



APPENDIX B 



Table II — Conlinued 



Food 



Honey .... 

Horseradish . . . 

Huckleberries . . 

Huckleberry wine 

Jam * 

JeUy 

Kohl-rabi . . . 

Lamb (See Meat) 

Leeks 

Lemons .... 

Lemon juice . . . 

Lemon, sweet . . 

Lentils, dry . . . 

Lettuce .... 

Limes 

Lime juice . . . 

Linseed meal . . 

Lupins, dry . . . 

Macaroni . . . 

Mackerel (See Fish; 

Mamey .... 

Mango .... 

Mangolds . . . 

Maple syrup . . 

Meat t 

Meat extract, solid 

Meat peptone . . 

Milk (cow's), whole 
(cow's), skimmed 
(cow's), con- 
densed . . . 



^^ 



.004 
.096 
.020 
.009 

.014 
.077 

.058 
.036 
.024 
.030 
.107 
•043 
•055 



•413 
.191 
.022 

.009 
.021 
.026 
.107 

.085 

.025 

.120 

(.122) 

(■300) 



SB 



.018 
•039 
.007 
.004 

(.010) 
.030 

.014 
.007 
.010 
.006 
.101 
.017 
.014 



•432 
.191 
•037 

.012 
.007 
.030 
•034 

•363 
.124 
.012 
(.012) 

(•032) 



< — 



386 
468 

051 
042 

100) 
370 

199 

175 
127 
442 
877 
339 
350 



083 
840 
130 

345 
23s 
334 
208 

347 
440 

143 
149) 

374) 






.001 
.062 
.016 
.006 

(■013) 
.050 

■.081 
.004 
.009 

.062 
.027 
.062 



.251 

•073 
.008 



.071 
.010 

2-394 

.641 

.051 

(-052) 

(.134) 



.019 
.076 
.008 
.004 

.008 
.071 

.006 
.022 
.010 
.042 
•438 
.042 
.036 



.741 
.520 
.144 

.028 
.017 
.038 
•013 

2.800 
1. 130 
•093 
(.096) 

235 



.029 
.016 
.008 
.001 

(.004) 
•053 

.024 
.002 
.003 
.013 
.050 
.074 
•039 



.08s 
•034 
•073 

.140 
.019 
.082 

(.010) 

3-II7 
.561 
.106 

(.110) 

(.280) 



to — 



«t. 



.001 .0007 
.190 

.Oil I .0009 
.006 

(007) (.0003) 

.05 7 .0006 



.072 
.011 
.006 
.016 
.277 
.014 
.010 
.003 
•396 

.172 



.013 
.026 

(■005) 



034 

(•035) 

(.090) 



.0006 



.0086 
.0007 



(•003) 



.00024 
.00025 

.0006 



* The perceatages of the ash constituents in jams are believed to average about 
two thirds those of the corresponding fruits. 

t Average meat is estimated to contain per 100 grams protein as follows: 0.058 
gram Ca; 0.118 gram Mg; 1. 6g4 grams K; 0.421 gram Na; 1.078 grams P; 0.378 
gram CI; 1.146 grams S; 0.0153 gram Fe. 



APPENDIX B 



42s 



Table II — Continued 



Food 



Milk — Cont. 

buffalo 203 

camel's . . . .143 

goat's 128 

human . . . .034 

mare's 083 

sheep's 207 

Millet 014 

Molasses 211 

Mushrooms . . . .017 
Muskmelon . . . .017 

Mustard 492 

Mutton (See Meat) 

Oatmeal 069 

Okra 071 

Olives 122 

Onions 034 

Oranges 045 

Orange juice . . .029 

Oysters 052 

Paprika 229 

Parsnips 059 

Peaches 016 

dried 034 

Peanuts 071 

Pears 015 

Pear juice . . . .009 
Peas, dried . . . .084 

fresh 028 

Pecan nuts . . . .089 
Pepper, green, fresh .006 
Pepper, black, dry .440 
Pepper, white, dry .425 
Perch (See Fish) 
Persimmons . . . .022 
Pineapple . . . .018 
Plums 030 



.016 
.021 

•013 
.005 
.007 
.008 
.167 
.068 
.016 
.012 
.260 

.110 
.010 
.002 
.016 
.012 
.011 

•037 
.164 

•034 
.010 
.056 
.180 
.011 
.008 
.149 
.038 
•152 
.010 
.156 
• 113 

.009 
.011 
.011 



.099 
.114 
■ 14s 
.047 
.081 
.187 
.290 
1-349 
•384 
•235 
.761 

•344 
•035 

1.526 
.178 
.177 
.182 
.091 

2.075 
.518 
.214 

(.830) 
•654 
.132 
.140 

■903 

.285 

(•332) 

(•139) 

1. 140 



.292 
.321 
.203 



.038 
.019 
.079 
.010 
.010 
.030 
.085 
.019 
.027 
.061 
.056 

.062 

•043 
.128 
.016 
.012 
.008 

•459 
.178 
.004 
.022 
.082 
.050 
.016 

.104 
.013 



•131 



.011 
.016 
.org 



.125 
.098 
.103 
.CIS 

•054 
.123 

•327 
.044 
.108 
•015 

■755 

•392 
.019 
.014 

■045 
.021 
.016 
•155 
•341 
.076 
.024 
.146 

•399 
.026 
.011 
.400 
.127 

•335 
.026 
.188 
•233 

.021 
.028 
.032 



2^ 

oi — 
qu 



.062 
.105 
.014 

•03s 
.029 
.071 
.019 

•317 
.021 
.041 
.016 

.069 

.004 
.021 
.006 
.003 
•590 
•155 
•030 
.004 

.056 
.011 

•035 
.024 
.050 
.013 
.312 
.029 

.002 
•051 



■037 



.129 

•051 
.014 
1.230 

.202 

.027 
.070 
.Oil 

.009 

.187 

.036 

.009 

.212 
.224 
.010 
.009 
.219 
.063 

•113 
.014 



.005 
.009 
.OOQ 



.0073 
.0003 

.0038 

.0029 
.0006 
.0002 
.0002 

.0045 

.0006 
.0003 
(.0012) 
.0020 
.0003 

.0057 
.0017 
.0026 
.0004 



.0005 

.COO 5 



426 



APPENDIX B 



Table II — Continued 



Food 


6 




^5 


en 


is 
11 


u 

u 
u 


OS 

in 


II 


Pomegranate . . 


.011 


.005 


.063 


.085 


• los 


.003 





.0004 


Pork (See Meat) 


















Potatoes .... 


.014 


.028 


.429 


.021 


•058 


.038 


.030 


.0013 


sweet .... 


.019 


.028 


•397 


•039 


045 


.094 


.024 


.0005 


Prunes, dried . . 


•054 


■055 


1.030 


.069 


•105 


.017 


•037 


•0030 


Pumpkin .... 


.023 


.008 


(■320) 


.065 


•059 


— 


.021 


(.0008) 


Radishes . . . 


.021 


.012 


.218 


.069 


.029 


•054 


.041 


.0006 


Raisins .... 


.064 


.083 


.820 


•133 


.132 


.082 


•051 


.0021 


Raspberries . . . 


.049 


.024 


■173 


— 


.052 


— 


.017 


.0006 


Raspberry juice 


.021 


.016 


■134 


.005 


.012 


— 


.009 


— 


Rhubarb .... 


.044 


.017 


•325 


.025 


.031 


.036 


•013 


.0010 


Rice, brown . . . 


— 


— 




— 


.207 


— 


— 


.0020 


white .... 


.oog 


•033 


.070 


•025 


.096 


•054 


.117 


.0009 


Romaine (salad) . 


•045 


.032 


.306 


.016 


•053 


•073 


.019 


— 


Rutabagas . . . 


.074 


.018 


•399 


.083 


.056 


•058 


•083 


— 


Rye, entire . . . 


•055 


•130 


•453 


•03s 


•385 


•025 


.170 


.0039 


(See also Bread 


















and Flour) 


















Salmon (See Fish) 


















Sapato .... 


.026 


.008 


.179 


— 


.006 


.087 


— 


— 


Shredded wheat 


.041 


.144 




— 


•324 


— 


— 


.0045 


Shrimp .... 


.006 














. . 








Soup, canned . . 


.036 


— 


•033 


— 


.030 


— 


— 


— 


canned vegetable 


.025 


.013 


.101 


— 


•038 


— 


•02 s 


— 


Spinach .... 


.067 


•037 


•774 


•125 


.068 


.074 


•038 


.0036 


Squash, summer, 


















seeds removed 


.018 


.008 


•150 


.002 


— 


— 


— 


(.0006) 


with seeds . . 


.024 


.012 


.180 


.004 


— 


— 


— 


(.0006) 


Squash, winter . . 


.019 


.oil 


•320 


.004 


— 


— 


— 


(.0006) 


Strawberries . . 


.041 


.019 


.147 


.050 


.028 


.006 


.014 


.0008 


Tamarind . . . 


.007 


.021 




— 


.072 


.007 


.009 


— 


Tapioca .... 


.023 





— 


— 


.090 


.018 


.029 


.0016 


Tomatoes . . . 


.oil 


.010 


•275 


.010 


.026 


•034 


.014 


.0004 


Tomato juice . . 


.006 


.010 


•310 


•015 


•015 


•055 


— 


— 


Truffles .... 


.024 


.018 


.404 


•077 


.062 


•039 


— 


— 


Turnips .... 


.064 


.017 


•338 


.056 


.046 


.041 


.065 


.0005 


Turnip tops . . 


■347 


.02S 


•30: 


.0S2 


.040' 


.I6S 


.060 


— 



APPENDIX B 



427 



Table II — Continued 



Food 


s 




SB 


li 

to 


a 

Bl? 

oS- 

CO 


is 


5 






Veal (See Meat) 


















Vinegar (cider) 


.016 


.008 


.165 


— 


•013 


— 


.017 


(.0003) 


Walnuts .... 


.080 


•134 
•034 


(.332) 
.287 


. 


.358 
.005 


.040 


.172 


.0021 


Water cress . . . 


.187? 


.099 


.061 


.167 


.0019 


Watermelon . . 


.Oil 


.003 


■073 


.008 


.003 


.008 


.007 




W^heat, entire . . 


•045 


•133 


•473 


■039 


•423 


.068 


.181 


.0050 


(See also Bread 


















and Flour) 


















Wheat bran . . . 


.120 


•511 


1. 217 


•154 


1.215 


.090 


•247 


.0078 


Wheat germ . . 


.071 


•342 


.296 


.722 


1.050 


.070 


■325 


— 


Wheat gluten . . 


.078 


•04s 


.007 


.028 


.200 


.050 


.920 


— 


Whey 


.04.4 


.008 


•157 


.038 


■035 


.119 


.009 


? 


Whortleberries, en- 








tire .... 


.031 


.021 


.261 


.021 


.042 


— 





— 


flesh only . . . 


.020 


.oil 


.087 




.018 


— 


— 


— 


Wine (avg.) . 


.000 


.010 


.104 


.008 


•015 


.011 


.015 


(.0003) 









TABLE III 

Protein, Calcium, Phosphorus, and Iron in Grams per 100 Calories 
OF Food Material 

(Estimated from data compiled from various sources) 



Food 


Protein 


Cal- 
cium 
(Ca) 


Phos- 
phorus 
(P) 


Iron 
(Fe) 


CaO 


P2O5 




Grams 


Grams 


Grams 


Grams 


Grams 


Grams 


Almonds 


3-22 


•037 


.072 


.00060 


.052 


.165 


Apples 


0.64 


.012 


.020 


.00048 


.016 


•045 


Apricots 


1.90 


.023 


.044 


.00052 


•033 


(.100) 


Asparagus 


8.10 


.122 


.177 


.00451 


.171 


•405 


Bacon (See Meat) 















428 



APPENDIX B 









Table III 


- - Continued 








Food 


Protein 


Cal- 
cium 
(Ca) 


Phos- 
phorus 
(P) 


Iron 
(Fe) 


CaO 


P2O6 




Grams 


Grams 


Grams 


Grams 


Grams 


Grains 


Bananas . 


1.32 


.009 


•031 


.00061 


.012 


.072 


Beans, dried . . . 








6.52 


.047 


•137 


.00203 


.065 


•314 


kidney .... 








S-83 


(.040) 


(•143) 


(.00216) 


(.056) 


(.326) 


Lima .... 








5.80 


.020 


.096 


.00200 


.028 


.221 


string .... 








5-55 


.110 


.126 


.00265 


•154 


.289 


Beef (See Meat) 




















Beer 








- — 


.008 


.061 


.00217 


.Oil 


.140 


Beets 








347 


.064. 


.084 


.00130 


.089 


•193 


Blackberries . . . 








2.25 


.029 


.058 


.00104 


.042 


•133 


Blueberries . . . 








(0.8) 


(.027) 


(.011) 


(.0012) 


(.038) 


(.025) 


Bluefish (See Fish) 




















Bread, Boston bro\\ 


n . 






2.64 


.056 


.082 


(.0013) 


.079 


.187 


"entire" wheat . 








3-95 


(.020) 


.071 


(.00065) 


(.028) 


(.163) 


graham . . . 








3.42 


(.020) 


.084 


(.00096) 


(.028) 


(.192) 


rye 








3-54 


.009 


.058 


.00039 


•013 


■^33 


white .... 








3-50 


.oil 


•035 


.00035 


•oiS 


.081 


Brussels sprouts 








(7-30) 


(.086) 


(•380) 


(.00349) 


(.121) 


(.870) 


Buckwheat flour 








i.8s 


.011 


.065 


.00034 


•015 


.148 


Butter .... 








0.13 


.002 


.002 


.00003 


.003 


.005 


Buttermilk . . 








8.40 


.294 


.271 


.00070 


.411 


.621 


Cabbage . . . 








5-07 


•143 


.092 


.00349 


.200 


.210 


Cantaloupe . . 








I-5I 


.044 


.038 


.00071 


.061 


.088 


Carp (See Fish) 




















Carrots . . . 








2.42 


.124 


.101 


.00133 


•173 


.232 


Cauliflower . . 








5-9° 


•403 


.200 


.00197 


•564 


•459 


Celery .... 








1.28 


.421 


.201 


.00270 


.589 


.460 


Chard .... 








8.37 


■393 


•105 


(•00655) 


•550 


.240 


Cheese 








6.05 


.212 


.156 


.00030 


.297 


■357 


Cherries . . . 








1.20? 


.025 


•039 


.00051 


•035 


.090 


Chestnuts . . 








2-55 


.014 


.044 


.00029 


.019 


.088 


Chicken (See Meat 




















Chocolate . . . 








2. II 


■015 


•07s 


(.00044) 


.021 


.171 


Citron .... 








0-15 


•037 


.010 


.00099 


.052 


.023 


Clams, long . . 








19.82 


.285 


.282 


(.00970) 


•399 


.645 


round . . . 








14.01 


.229 


.100 


(.00970) 


■321 


.228 


Cocoa .... 








4-35 


.023 


■143 


.00054 


.032 


■327 


Coconut . . . 








0.9s 


.006 


.018 


(.00030) 


.009 


.041 


Cod (See Fish) 








' 







APPENDIX B 



429 



Table III — Continued 



Food Protein 


Cal- 
cium 


Phos- 
phorus 


Iron 
(Fe) 


CaO 


P2O5 






(Ca) 


(P) 








Grams 


Grams 


Grams 


Grams 


Grams 


Grams 


Corn 


3.06 


.006 


.102 


.00079 


(.008) 


(.233) 


Corn meal .... 




2-59 


.005 


•O.S3 


.0003 


.007 


.121 


Cotton-seed meal . . 




12.80 


.066 


.298 


— 


.092 


.682 


Cowpeas 




6.20 


.029 


.132 


— 


.041 


■303 


Crackers, "soda" . . 




2.37 


.006 


.025 


.00036 


.008 


•057 


Cranberries .... 




0.85 


•039 


.027 


.00129 


•054 


.062 


Cream, 18.5 per cent fat 




1.27 


.050 


.044 


.0001 


.072 


.100 


40 per cent fat . . 




0.58 


.020 


.020 


.00005 


.032 


•045 


Cucumbers .... 




4.60 


.090 


.191 


.00115 


.126 


•437 


Currants, dried (Zantc) 




0-7S 


.026 


.061 


.00087 


.036 


• 139 


fresh 




2.62 


•045 


.066 


.000S7 


.063 


•150 


Dandelion greens . 




3-93 


.172 


.117 


.0044 


.241 


.269 


Dates 




0.60 


.019 


.016 


.00086 


.026 


.037 


Duck (See Meat) 
















Eggplant 




4-3° 


.041 


.122 


.00184 


•057 


.280 


Eggs • 




9-05 


•04s 


.122 


.00205 


.063 


.279 


Egg white .... 




24.12 


.020 


.022 


.00020 


.028 


.050 


Egg yolk 




4-32 


.036 


.118 


.00230 


.050 


.270 


Farina 




3-05 


.006 


•035 


.00022 


.008 


.079 


Figs 




1 1-35 


•051 


•037 


.00095 


.072 


.084 


Fish (See footnote on page 












423) 












Flour, buckwheat .... 


1.84 


.Oil 


.065 


.00034 


•015 


.148 


"entire" wheat . . 




3.85 


.009 


.066 


.0007 


.012 


•152 


graham 




3-71 


.oil 


.101 


.00100 


■015 


.232 


white (wheat) . . 




3.20 


.006 


.026 


.00023 


.008 


.060 


rye 




i 1-95 


.005 


.082 


.00037 


.007 


.188 


Fowl (See Meat) 












Goose (See Meat) 












Grapefruit 1.15 


.040 


.036 


.00058 


.056 


.083 


Grapes 


1-35 


.019 


.032 


.0003 1 


.027 


.074 


Grapejuice 


0-35 


(.oil) 


.on 


.0003 


•015 


.025 


Haddock (See Fish) 














Halibut (See Fish) 














Ham (See Meat) 














Hazelnuts 





.041 


.o%o 


.00057 


•057 


.115 


Herring (See Fish) 




•^ J^ 




Hominy . 2.3=; 


.002 


.027 


.00025 


.002 


.063 



430 



APPENDIX B 



Table III — Continued 







Cal- 


Phos- 


Iron 
(Fe) 






Food 


Protein 


cium 
(Ca) 


phorus 
(P) 


CaO 


PK). 




Grams 


Grains 


Grams 


Grams 


Grams 


Grams 


Honey 


0.12 


.002 


.006 


.0003 


.002 


•013 


Huckleberries 


0.82 


.027 


.Oil 


.0012 


.038 


.025 


Kohl-rabi 


6.48 


.249 


.186 


.00194 


•349 


.426 


Lamb (See Meat) 














Lemons 


2.25 


.081 


.049 


■00135 


•113 


.112 


Lemon juice 


— 


.060 


— 


— 


.084 


•059 


Lentils 


7-37 


•031 


.126 


.00247 


•043 


.288 


Lettuce 


6.27 


.224 


.224 


.00785 


•314 


•513 


Linseed meal 


— 


— ■ 


— 


— 


— 


— 


Lupins 


— 


— 


— 


— 


— 


— 


Macaroni 


3-70 


.006 


.040 


•00033 


.008 


.092 


Mackerel (See Fish) 














Maple syrup 


— 


■037 


(■003) 


(.001) 


•053 


(•007) 


Meat (See footnote on page 














424) 














Milk, whole 


4-75 


.174 


•134 


.00035 


•243 


.308 


skimmed 


9-25 


(.331) 


.262 


(.00068) 


(.463) 


(.600) 


condensed, sweetened . . 


2.70 


(.096) 


.072 


(.0002) 


(•135) 


.165 


condensed, unsweetened . 


5-75 


.189 


.146 


(.0004) 


(.264) 


•335 


Molasses 


0.83 


.074 


•015 


•00255 


.102 


•035 


Muskmelon 


I-5I 


•043 


.038 


.0008 


.060 


.088 


Mutton (See Meat) 














Oatmeal 


4.20 


.017 


.099 


.00096 


.024 


.226 


Olives 


0.37 


.041 


.004 


.00097 


•057 


.010 


Onions 


3-30 


.069 


■093 


.0010 


.097 


.212 


Oranges 


1-55 


.088 


.040 


•00039 


•123 


.091 


Orange juice 


1.44 


.067 


•037 


.00046 


•093 


.082 


Oysters 


12.30 


.106 


.306 


.00893 


.149 


.702 


Parsnips 


2.47 


.091 


.117 


.0009 


.128 


.268 


Peaches 


1.70 


.038 


•057 


.00073 


•053 


.130 




4.70 


.013 


•073 


.00036 


.018 


.166 


Pears 


0-95 


.024 


.041 


.00047 


•033 


•093 


Peas 


6.92 


.026 


.120 


.00165 


•036 


.274 


Pecans 


1.30 


.012 


•045 


•00035 


.017 


.104 


Pepper, green 


4-59 


•034 


•145 


.00222 


•047 


■333 


Perch (See Fish) 














Persimmons 


— 


— 


— 


— 


— 


— 


Pineapple, fresh .... 


0.92 


.041 


.064 


.00116 


•058 


.146 



APPENDIX B 



431 



Table III — Continued 



FOOE 


Protein 


Cal- 
cium 
(Ca) 


Phos- 
phorus 
(P) 


Iron 
(Fe) 


CaO 


F^Os 




Grams 


. Grams 


Grams 


Grams 


Grams 


Grams 


Plums . . . 


. . . . 1.20 


.024 


.038 


.00059 


•033 


.087 


Pork (See IMeat) 














Potatoes . . 


.... 2.65 


.016 


.069 


.00156 


.023 


.158 


sweet . 




.... 1.45 


.016 


•037 


.00041 


.023 


.084 


Prunes . . 




. . . . 0.70 


.018 


•035 


.00100 


■025 


.080 


Pumpkin . 




.... 3-90 


.089 


.229 


(.00130) 


.125 


•525 


Radishes . 




.... 4.42 


.073 


.098 


.00205 


.102 


.225 


Raisins 




.... 0.75 


.019 


.038 


.00139 


.026 


.088 


Raspberries 




.... 2.57 


.074 


.078 


.00091 


.104 


.178 


Rhubarb . 




. . . . 2.60 


.189 


•134 


•00433 


.264 


•307 


Rice, brown 




.... 2.52 


(.003) 


.060 


.00058 


(.004) 


.138 


white 




. . ." . 2.27 


.001+ 


.027 


.00026 


.003 


.063 


Rutabagas 




.... 3-15 


.185 


.140 


— 


.259 


.322 


Rye, entire 




. . . . — 


— 


— 


— 


— 


— 


Salmon (See Fisl 


1) 












Shredded wheat 


• . . • 3.50 


.Oil 


.089 


.00123 


.016 


.203 


Spinach . . 


.... 8.79 


.281 


.285 


.01506 


■393 


•653 


Squash, summer 


.... 3-05 


■039 


•03s 


(.0013) 


■054 


.080 


winter . . 


.... 3.10 


.040 


.061 


(.0013) 


.056 


•139 


Strawberries 




.... 2.56 


.104 


.072 


.00205 


.146 


.164 


Tapioca . 




. . . . O.II 


.004 


.025 


.00045 


.006 


.058 


Tomatoes 




.... 3-95 


.050 


■113 


.00175 


.070 


•259 


Turnips . 




.... 3.30 


.161 


.117 


.00127 


.226 


.269 


Turnip tops 




. . . . — 


— 


— 


— 


— 


— 


Veal (See Meat) 














Vinegar (cider) 


. . . . — 


.Ill 


.090 


.00213 


.156 


.206 


Walnuts, Califor 


nia or Eng- 












lish . . 


. . . . 2.60 


•013 


•015 


.00030 


.018 


.116 


Water cress . 


. . . . — 


— 


— 


— 


— 


— 


Watermelon . 


.... 1.32 


.038 


.010 


(.00099) 


•053 


.023 


Wheat, entire 


.... 3-63? 


•013 


.118 


.00140 


.018 


.270 


Wheat germ . . 






— 


— 


— 


— 


Wheat gluten 


.... — 


— 


— 


— 


— 


— 


Whey . . . . 


.... 3.74 


.165 


•131 


? 


.231 


.300 


Whortleberries . 


. . . . — 


— 


— 


— 


— 


— 


Wine (average, 


10 per cent 












alcohol) . 




1 


.oil 


.021 


.00167 


.016 


.047 



INDEX 



Abderhalden, 

amino acids in blood, 120 

inorganic iron in nutrition, 203-295 

physiological chemistry, 136, 257, 308 

sulphides in alimentary canal, 293 
Abel, amino acids dialyzed from blood, 

120 
Abel, Rowntree, and Turner, removal 
of diffusible substances from 
blood of living animals, 136 
Absorption in small intestine, 93 
Acetic acid, 108, 109 

aldehyde, 108, 109 
Acetoacetic acid, 116 
Acetone bodies, 117 
Acetonitrile poisoning, effect of diet 

on resistance to, 350 
Acid, acetic, 108, 109 

acetoacetic, 116, 126 

adenylic, 132 

a-ketonic, 216 

amino, 43-48, 55-68, 119-122, 216, 217 

aminoglutaric, 44 

aminosuccinic, 44 

aspartic, 44, 47, 60, 61, 120, 126 

/3-hydroxy, 116 

^-ketonic, 116 

|8-oxj^butj'ric, ii6 

butyric, 22, 113, 116 

capric, 22 

caproic, 22, 116 

caprylic, 22 

carbonic, 108, 109, 275, 276 

diamino, 44, 67 

diaminomonocarboxylic, 44 

diaminotrioxydodecanic, 61 

crucic, 23 

fatty, see Fat 

formic, 108, 109 

glutamic (glutaminic), 44, 47, 60, 61, 
120, 126 

guanylic, 132 

hypogasic, 23 



Acid — Continued 

lactic, 75, 105, 109, 113, 124, 126, 216 

lauric, 22, 116 

linoleic, 24 

linolenic, 24 

monoaminodicarbox>'lic, 44 

monoaminomonocarboxylic, 43 

myristic, 22, 116 

nicotinic, 327 

nucleic, 130-137 

octoic, 113, 114 

oleic, 23 

palmitic, 22, 116 

phosphoric, 131, 132 

phycetoleic, 23 

phytic, 244 

pyruvic, 108, 109, 114, 125, 216 

stearic, 22, 116, 216 \ 

Acid-forming diet, 279, 282 
Acid-forming and base-forming ele- 
ments in food, 279-283 
Acidity, 76, 77, 274 
Acidosis, 117, 179, 280 
Ackroyd and Hopkins, deficiencies in 

amino acid supply, 136, 355 
Acrolein, 19 

Activating substances, 76 
Activity, muscular, 179-188, 226-229 
Adenine, 131, 132, 327 

isomer of, 327 
Adenosine, 132 
Adenylic acid, 132 
Agar-agar, 17 

..Age, influence on food requirement, 
193-198, 229-233, 370-373 

on protein metabolism, 229-233 
Alanine, 43, 45, 47, 48, 60, 61, 120, 124, 
125, 126, 216, 403 

deamination of, 126, 216, 403 
Albumins, 52, 54, 56, 60, 142, 404 
^ acid-, 54 

alkali-, 54 

coagulated, 54, 73, 406 



2 F 



433 



434 



INDEX 



Albuminates, 54 

Albuminoids, 404 

Albumoscs, src Proteases 

Alcohol-soluble proteins, 52, 56, 404 

Aldoses, 3, 4, 5 

Aldrich, chemical nature of pepsin, 72 

Alexis St. Martin, observations upon, 

70 
Alimentary glycosuria, 6 
Alkali (Alkaline) reserve, 280, 313 
Alkalinity, 76, 77, 274 
Allantoin, 323 

Allen, metabolism in diabetes, 136 
Allose, 5 
Almonds, 146, 256, 26g, 302, 395, 410, 

421, 427 
a-ketonic acid, 216 

aldehyde, 120 
Altrose, 5 
Amandin, 52, 60 

Amino acids, 43-48, 55-68, 1 19-122, 
126, 216, 217 

absorption of, 1 20 

dialyzed from blood, 120 

disappearance of, 121 

formation of, 125 

saturation capacity of tissues for, 121 

separation of, 120 

yields of 

from flesh, 61 
from proteins, 60-61 
Aminooxypurine, 132 
Aminopurine, 132 
Aminoglutaric acid, 44 
Aminolipins, 36 
Aminosuccinic acid, 44 
Ammonia, relation to nitrogen metabo- 
lism, 130, 136, 216, 284 

to regulation of neutrality, 126, 278, 
279, 281, 283 
Ammonium carbamate, 129 

carbonate, 129 
Amylases, 73, 74, 76, 103 
Amylolytic enzymes, see Amylases 
Amylopectin, 13 
Amylopsin, 76 

in pancreatic juice, 73, 90 

occurrence and action of, 79 
Amylose, 13 

a-amylose, 13 
Anaerobes, 97 



Anderson, organic phosphoric acid com- 
pound of wheat bran, 257 
Anderson and Lusk, relation between 
diet and energy production dur- 
ing work, 200 
Antineuritic action, relation of chemical 
structure to, 326 
substances, attempts to isolate, 323, 
324 
Antipcristalsis, 94 

Antiscorbutic property, of food, 310, 
311-318 
effect of cooking upon, 314, 315 
Appetite, 80, 81 

as dietary standard, 361 
Apples, 146, 256, 269, 302, 395, 410, 

421, 427 
Apricots, 410, 421, 427 
Arabans, 5 
Arabinose, 4 
Araboketose, 4 
Arachin, 52 
Arginine, 44, 47, 60, 61, 72, 120, 126, 

129, 403 
Armsby, animal nutrition, 168, 200 
experiments in heat production, 162, 

164 
food as body fuel, 168 
food supply of the future, 400 
Armsby and Fries, influence of standing 

or lying on metabolism, 200 
Aron, calcium requirement of children, 
282 
experiments with limited rations, 338 
nutrition and growth, 355 
phosphorus in beriberi, 322 
Aron and Frese, utilization of different 

forms of food calcium, 282 
Aron and Sebauer, calcium for growing 

organism, 282 
Artichoke, 410 
Ash constituents, xii, 234-309, 342-345, 

382, 391-401, 409, 421-431 
Asparagus, 146, 394, 410, 421, ^127 
Aspartic acid, 44, 47, 60, 61, 120, 126 
Asymmetry of underfed animals, 338 
Atwater, bomb calorimeter, 139, 140 
chemistry and economy of food, 168, 

400 
coeflScients of digestibility in mLxed 
diet, loi 



INDEX 



435 



Atwater — Continued 

dietary standards, i8o, 36,3, 365, 400 

muscular work and protein metabo- 
lism, 228 

protein sparing action of carbo- 
hydrate and fat, 214, 215 

respiration calorimeter experiments, 
168, 200, 400 
Atwater and Benedict, fats and carbo- 
hydrates as protectors of protein, 
232 , 

mechanical efiSciency of man, 183, 

i8s 
metabolism during sleep and sitting 

at rest, 176 
metaboUsm while fasting, 188 
respiration calorimeter, 168 
rest experiments, 164-166 
Atwater, Benedict, et al., respiration 

calorimeter experiments, 200 
Atwater-Rosa-Benedict, respiration calo- 
rimeter, 158-163 
Atwater and Snell, bomb calorimeter, 

i3g, 140, 168 
Aub and DuBois, basal metabolism of 
old men, 200 

Babcock, metabolic water, 257 
Bacillus, aerogenes capsulatus, 97 
bifidus, 96 
coli, 96, 97 
lactis aerogenes, 96 
Bacon, 146, 394, 410, 421, 427 
Bacteria, in digestive tract, 95, 97-98 
Bailey and Murlin, energy requirement 

of new-born, 200 
Bananas, 146, 256, 269, 302, 395, 410, 

421, 428 
Barley, 410, 421 
Barlow's disease, 316 
Baumann and Howard, mineral metabo- 
lism of scurvy, 327 
Bayhss, general physiology, 102, 257 

nature of enzyme action, 102 
Bayliss and StarUng, secretin, 91 
Beans, 146, 241, 256, 269, 302, 321, 

394, 410, 421, 428 
Beaumont, observations upon Alexis 
St. Martin, 70, 71 
on stomach contraction, 83, 84 
Bed calorimeter, 160, 162, 167 



Beef, 6t, 145, 241, 256, 269, 302, 394, 

411, 412, 421, 428 
Beer, 421, 428 

Beets, 146, 394, 412, 421, 428 
Beet sugar, see Sucrose 
Benedict (F. G.), metabolism during 
fasting, 200, 232, 239, 257, 263, 
272, 273, 282 
in relation to acidosis, 179 
muscular work, 200 
pulse rate, 175, 176 
variations in metabolism, 179 
nutritive requirements of body, 378, 

400 
per unit of area, 172 
respiration apparatus, 151, 152, 168 
Benedict (F. G.) and Carpenter, metabo- 
lism experiments, 176, 177, 178, 200 
respiration calorimeter, 168 
Benedict (F. G.) and Cathcart, metabo- 
lism during muscular work, 187, 
188, 200 
Benedict (F. G.) and Emmes, basal 
metabolism of men and women, 
201 
influence of non-oxidizable material 
upon metabolism, 200 
Benedict (F. G.) and Murschhauser, 
metaboUsm during muscular work, 
182, 183 
Benedict (F. G.) and Osterberg, human 

fat, 30 
Benedict (F. G.) and Roth, energy 
metabolism of vegetarians, 190, 
191, 201 
Benedict (F. G.) and Smith, metabolism 

of athletes, 201 
Benedict (F. G.) and Talbot, energy 
metabolism in infants, 195 
respiratory exchange of infants, 201 
Benedict (S. R.), uric acid in metabo- 
lism, 136 
Beriberi, 310, 318-324, 327-330 
Berthelot, bomb calorimeter, 139 

mixed glycerides, 26 
Betaine, 327 
/3-amylose, 13 

/3-hydroxy acids in fat metabolism, 116 
/3-ketonic acid, 116 
iS-oxidation theory, 116, 216, 217 
/3-oxybutyric acid, 116 



436 



INDEX 



Bile, 9 1 

Blackberries, 412, 421, 428 
Blacklish, 412 

Blatherwick, effect of base-forming ele- 
ments in food, 281, 282 
Blauberg, mineral metabolism of in- 
fants, 282 
Blood, ash of, 421 
glucose content of, 6, 104, 118 
reaction of, 273-284 
see also Amino acids 
Bloor, metabolism of fat, 34, 40 
Blueberries, 421, 428 
Bluefish, 412, 428 
Blyth and Robertson, mixed glyccride 

of butter fat, 26 
Body fat, composition of, 30-35, 142 

influence of food fat, 32-34 
Body, human, elementary composition 

of, 234 
Body temperature, regulation of, 191- 

193, 202 
Boldireff, on hunger, 82 
Bomb calorimeter, 139, 140 
Bomer, mixed glycerides, 26 
Bones, calcification and development 
of, 343 
source of calcium for carnivora, 262 
Boutwell, phytic acid of wheat kernel, 

2S7 

Braddon, cause and prevention of 
beriberi, 319, 327 

Braddon and Cooper, carbohydrate and 
vitamine metabolism, 325, 328 

Brazil nuts, 412 

Bread, 146, 299, 394, 413, 421, 428 

Breadfruit, 421 

BreadstufTs, see Grain products 

Brcithaupt and Cetti, calcium elimina- 
tion, 263 

British gum, 14 

Browne, butter fat, 32, 40 
definition of sugar, 2 

Brussels sprouts, 421, 428 

Buckwheat flour, 413, 421, 428 

Bunge, metabolism of iron, 287, 288, 
292, 293, 300, 301, 305, 306 
physiological and pathological chem- 
istry, 257, 308 
sodium chloride ehmination, 23S 
ase of salt, 238 



Bunge and Abderhalden, phosphorus 
content of milk, 247, 248 

Bureau of markets, 399 

Butter, 21, 22, 146, 386-392, 394, 413, 
421, 428 

Butter fat, 31-32, 142, 346, 356-358 
growth promoting property of, 346, 
356-358 

Buttermilk, 413, 421, 428 

Butternuts, 413 

Butyric acid, 22, 113, 116 

Cabbage, 146, 269, 302, 395, 413, 422, 

428 
Cxcum, 94 

CafTeine, effect on metabolism, ref., 202 
Calcium, 234, 260-272, 343, 344, 383, 
391-396, 421-431 
amounts in dietaries, 267, 268 
amounts in foods, 268, 269, 421-431 
elimination, 263 
function in body, 260, 261 
in milk, 268 
relation to metabolism of iron, 270, 

298-299, 382-383 
requirement, 262-268 
of children, 265, 266 
of women, 264, 265 
Calf's foot jelly, 413 
Calorie, 139, 140 
Calorimetrj', direct, 15S 

indirect, 154 
Camerer, calcium requirement at dif- 
ferent ages, 266 
storage of food for growth, 194 
Camerer and Soldner, ash constituents 
of new-born infant and human 
milk, 282 
Cane sugar, see Sucrose 
Cannon, action of pylorus, 86 

competency of ileocecal valve, 94 
explanation of hunger, 81, 103 
intestinal digestion, 90 
mechanical factors of digestion, 102 
movements of stomach and intestines 

during digestion, 84 
passage of food through small intes- 
tine, 92, 93 
psychic contraction, 88 
Cannon and Washburn, investigation 
of hunger, 80, Si, 82, 103 



INDEX 



437 



Canteloupe, 422, 428 

Capers, 422 

Capric acid, 22 

Caproic acid, 22, 116 

Caprylic acid, 22 

Carbohydrates, 1-18, 131, 142, 143 

classification, 2, 4-5 

conversion into fat, iii, 112 

fermentation of, 97 

formation from fat, 117, 118 

formation from protein, 123, 124 

metabolism of, 104-115, 123-125, 
136-137 

oxidation of, 105 

references, 17, 18 

respiratory quotient of, no, in 

storing of, in 

synthesis of, i, 2 

yield from protein, 124-127 
Carbon, 234 

Carbon and nitrogen balance, 115, 156 
Carbonic acid, 108, 109, 275, 276 
Carlson, hunger in health and disease, 
84, 103 

hydrochloric acid in gastric juice, 87 
Carpenter, metabolism increase during 
tj'pewriting, 201 

respirator>' exchange, 169 
Carpenter and Murlin, metabolism of 

■ mother and child, 201 
Carrots, 146, 256, 269, 302, 395, 413, 

422, 428 
Casein, 47, 48, 49, 53, 58, 61, 64, 73, 
142, 225, 226, 240, 243, 246, 339, 
340, 354 
Caseinogen, 53 ; see also Casein 
Catalysts, organic, 75 
Catalyzers, 78, 79 
Cathcart, protein metabolism, 232 
Cauhflower, 413, 422, 428 
Caviar, 422 

Celery, 146, 395, 413, 422, 428 
Cellulose, 5, 15 
Cerealine, 413 
Cereals, see Grain products 
Cetti and Breithaupt, metabolism of 

iron while fasting, 298 
Chamberlain, beriberi, 320, 321, 323, 328 
Chamberlain and Vedder, etiology of 
beriberi, 328 
rice polishings in beriberi, 322 



Chard, 413, 422, 42S 

Cheese, 256, 269, 302, 386-392, 394, 

413, 422, 428 
Chemical composition of foods, 407- 

431 
Cherries, 413, 422, 428 
Chestnuts, 146, 414, 422, 428 
Chick and Hume, distribution among 

foodstuffs of substances required 

for prevention of beriberi and 

scurvy, 328 
Chicken, 61, 414, 422, 428 
Children, food requirements of, 193- 

198, 200-202, 229-233, 265-268, 

300, 331-347, 355-35Q. 370-373. 

381-383, 400 
table of weights and rates of growth, 

372, 373 
Chinese moss, 17 
Chittenden, dietary standard, 366, 

376, 379 
economy in nutrition, 232, 400 
low protein metabolism, 376 
nutrition of man, 232, 400 
protein requirement, 218-220, 376, 

379 
Chittenden and Underbill, production 

of condition resembling pellagra, 

35S 
Chloride metabolism, 236, 237, 271, 272 V 
Chlorine, 234, 236, 237, 271, 272 
Chlorosis, 289, 290 
Chocolate, 414, 422, 428 
Cholesterol, 37, 91 
Choline, 323 
Chyme, 89 
Chymification, 71 
Cider, 422 

Circulation, work of, 168 
Citron, 422, 428 
Clams, 422, 428 
Cocoa, 395, 414, 422, 428 
Coconut, 422, 428 
Cod, 146, 414, 422, 428 
CoeiEcient of digestibility of food, 99, 

loi, 102 
Cold storage, 399 
Collagen, 52 

Colloidal platinum as catalyzer, 78 
Colloids, 12, 51 
Colon, 94 



438 



INDEX 



Combustion, heat of, 139-142 
Combustion in body, 109 
Common salt, use of, 236-238 
Comparison of cost and food value, 391- 

400 
Composite valuation, 391-396 
Composition of body, 156, 174, 175, 

234. 300, 301, 336-339 
Conarachin, 52 
Conjugated proteins, 53 
Consomme, 414 

Corn, 146, 302, 395, 414, 422, 429 
Cornflakes, 394 

Corn meal, 146, 394, 414, 422, 429 
Cottonseed meal, 3^3, 354, 422, 429 
Cowpcas, 414, 422, 429 
Crackers, 394, 412, 414, 422, 429 
Cranberries, 414, 422, 429 
Cream, 394, 414, 422, 429 
Creatine, 134, 135 
Creatinine, 134, 135, 142 
Cramer, production of fat from protein, 

127, 128 
Cresol, 98 

Cucumbers, 395, 414, 422, 429 
Currants, 146, 414, 422, 429 
Cystine, 35, 37, 43, 60, 61, 64, 126, 340 
Cytodine, 132 
Cytodinc-nucleotide, 132 
Cytosine, 131, 132, 133 

Dakin, beta oxidation theory, 116 
interrelations of protein and car- 
bohydrate, 124-127 
oxidations and reductions in animal 
body, T17, 136 

Dakin and Dudley, intermediary me- 
tabolism, 136 

Dandelions, 414, 423, 429 

Daniels and Nichols, nutritive value 
of soy bean, 355 

Darling, pathological affinities of beri- 
beri and scurvy, 328 

Dates, 305, 414, 423, 429 

Derived proteins, 53 

Descartes, fermentation in stomach, 60 

Dextrans, 5 

Dextrin, s, 14, 83, 86 

Dextrose, see Glucose 

Dezani, chemical nature of pepsin, 72 

(/.Fructose, see Fructose 



</. Glucose, see Glucose 

Diabetes, 116, 117, 136 

Diabetic sugar, see Glucose 

Diamino acids, 44, 67, see also Arginine, 

Histidine, Lysine 
Diaminomonocarboxj'lic acids, 44 
Diaminotrioxydodecanic acid from casein, 

61 
Diastase, see Amylase 
Dibbclt, calcium salts during pregnancy 

and lactation, 282 
Dicalcium phosphate, 247 
Dicysteine, 43 
Diet, see under Dietaries, Dietar>% also 

under Food 
Dietaries, 255-257, 267-268, 271, 303, 

360-401 
Dietarj- deficiencies, 310, 347-359, 384. 396 
Dietar>- standards, 361-367, 385 
Dietary studies, 149, 150, 364, 370, 371, 

389. 390 
DigestibiUty of food, 99-103 
Digestion, gastric, 85-87 
intestinal, 89-90, 93-94 
saHvary, 80, 82, 85 
Dihexoses, 5 
Dioses, 4 
Dioxyacetone, 4 
Dioxypurine, 132 
Dipeptids, 45-46 

Disaccharides, 4, 5, 8-1 1, 17-18, 79 
Disaccharoses, 4, 5, 8-11, 17-18 
Distribution of expenditures for food, 

386-390, 396-398 
"Double bonds," 23 
Doughnuts, 414 
Drying oils, 24 
DuBois, basal metabolism of man, 178, 

198, 201 
metabolism of boys, 196, 201 
respiration calorimetry, 201 
DuBois and Associates, metabolism in 

disease, 201 
DuBois and DuBois, formula to esti- 
mate surface area, 173, 201 
relation of body surface to metabolism, 

172, 173- 174 
table of surface areas, 173 
Duck. 423, 429 

Duclaux, terminolog>' for enzymes, 76 
I Duodenum, 89, 90 



INDEX 



439 



Eberle, artificial digestive juice, 71 
Eckles, efifect of sparse diet upon time 
required to reach maturity, 
338 
Economic use of food, 386-401 
Edestin, 49, 52, 56, 60, 142, 225, 226, 

240, 247, 339, 340 
Edie, et al., antineuritic bases, 328 
Efficiency, mechanical, of man, 181-185, 

200 
Effront, enzymes, 103 
Egg albumin, 49, 52, 55, 60, 240 
Egg white, 299 
Egg yolk, 256, 269, 302 
Eggplant, 414, 423, 429 
Eggs, 146, 241, 256, 269, 302, 386, 387, 
388, 389, 390, 391, 392, 414, 423, 
429 
Ehrlich and Lazarus, medicinal iron in 

hemoglobin formation, 297 
Ehrstrom, phosphorus metaboUsm in 

man, 247, 257 
Eijkmann, beriberi in fowls, 321, 322 
Elementary composition, 30, 32, 49, 

142, 156, 234, 421-431 
Embden and Schmitz, amino acid forma- 
tion, 125, 136 
Emmett and Grindley, phosphorus 

content of flesh, 257 
Emmett and McKim, yeast vitamine 
fraction as supplement to rice 
diet, 328 
Endive, 423 

Energy allowances for adults, 366, 367, 
370 
for children, 370-373 
expenditure, during muscular labor, 

185, 186 
metabolism, 148-201 

experimental methods, 148-169 
governing conditions, 170-201 
of growing infant, 195, 196 
influence of age and growth, 193, 

194 
influence of food, 188 
effect of internal secretions, 178 
influence of mental work, 177, 178 
requirement, 148-201, 366-373 
influence of sex, 199 
methods of study, 149-166 
Enterokinase, 92 



Enzymes, 6, 8, 10, 11, 69-80 

activity of, 75, 76, 77 

amylolytic, 75 

chemical nature of, 71 

classification of, 74 

coagulating, 75 

colloidal nature of, 72 

deaminizing, 75 

digestive, 69 

extracellular, 75 

hydrolytic, 75 

intracellular, 75, 103 

introduction of word, 74 

isolation of, 74 

lipolytic, 75 

properties of, 74 

proteolytic, 75, 97 

reducing, 75 

sugar-spHtting, 75 
Epigastrium, 81 
Eppler, investigations of phosphatids, 

258 
Erepsin, 80, 92 
Ergometer, 185 
Erucic acid, 23 
Erythrose, 4 
Erj^thrulose, 4 
Essential oils, 36 
Esterase, 103 

Ethereal sulphate, 98, 241, 242 
Ethylene linkage, 23 
Euler, chemistry of enzjTnes, 103 ' 
Evvard, Dox, and Guernsey, cystine, 
in tissue growth, 345 

effect of calcium and protein fed preg- 
nant swine on offspring, 282, 355 
Excelsin, 52, 60, 225 

Factors determining dietary standard, 
360, 361, 385 
for calculating energy requirement, 

186 
for calculating fuel values of food, 
143 

T'alck, influence of body fat upon pro- 
tein metabolism, 205, 206 

Falk and Siguira, lipase preparations, 
74. 103 

Falk, lipolytically active substances, 
74, 103 

Farina, 394, 415, 423, 429 



440 



IXDKX 



Fasting, iS8, i8g, 200, 203-206, 253, 

272, 273, 2g8 
Fats, 19-36, 40-41 

calories per gram, 142, 143 

composition of, 30-32 

fish, 24 

food, influence of, on body fat, 32-34 

formation from carbohydrates, 27- 

29, 112-115 
formation in nature, 27-29 
general properties, 19-21 
hardened, 23 
heart, 30-31 
hydrolysis of, ig 
kidney, 30-31 
liver, 30-31 
metabolism of, 115 
of organs, 30-3 1 
oxidation of, 115 
production from protein. 127 
respiratorj' quotient of, no, in 
storage in body, 117 
structure of, 19, 21-27 
Fatty acids, 21-24, 36 
in metabolism, 116 
unsaturated, 23-24, 31 
Fatty oils, 19, 36 
Fat soluble A, xiii, 333, 346, 347, 383, 

384; see also Growth 
Feces, 99, 100, loi, 103, 253, 254, 263, 

286, 289, 299 
Fermentation, 69, 97 
Ferments, 75 ; see also Enzymes 
Fibrin, 53 
Figs, 415, 423, 429 
Filberts, 395 
Fingcrling, phosphorus metabolism, 249 

250, 258 
Fischer, synthetic polypeptids, 46, 40- 

50 
Fischer and Abderhalden, diamino- 
trioxy-dodecanic acid from casein, 
61 
Fish, 386, 387, 389. 390, 391, 392, 423, 

429 
Fitz, Alsberg, and Henderson, excretion 
of phosphoric acid in acidosis. 
282 
Fixed oils, 19 
I'lesh, amino acids of, 61 
Fletcher, beriberi and rice, 320 



Flounder, 415 

Flour, 241, 256, 269, 302, 394, 41S, 423, 

429 
Fluorine, 234 

Folin, distribution of excreted nitrogen, 
135 
protein metabolism, 137, 376, 377, 400 
Folin and Denis, protein metabolism, 
137 
relation of amino acids to metabolism, 
119 
Food, allowances for healthy children, 
371 
analy.ses, 408, 409, 410-431 
antineuritic properties of, 310, 318- 

330 
antiscorbutic properties of, 310- 

318, 327-329 
composition of, 407, 408, 409, 410-431 
digestibility of, 99-103 
economic use of, 386-401 
fuel value of, xii, 138-147, 407-420 
functions of, xi, 335 
influence of, on growth, sec Growth ; 
on metabolism, 188-101 ; see also 
under names of the different food- 
stuffs 
nutritive ratio of, 147, 148 
passage through intestine, 92-94 
passage through stomach, 83-89 
requirements, 170-233, 252-267, 297- 
301, 331-385. 400- 401 
Foods, sec Food, sec also under name of 

each 
Foodstuffs, see under the name of each 

definition, xii 
Forbes, pho.sphorus, 242, 251, 258 
mineral elements in nutrition, 258, 

283 
effect of rations upon development 
of swine, 258, 355 
Forbes and Beegle, mineral metabolism 

of milch cow, 265, 283 
Forbes and Keith, functions of phos- 
phorus, 242, 243 
organic and inorganic phosphorus, 251 
phosphorus compounds in animal 
metabolism, 25S 
Formaldehyde, i, 2 
Formic acid, 108, 109 
Fowls, 415, 423, 429 



INDEX 



441 



Fraser and Stanton, study of beriberi 
due to use of polished rice, 320, 
322 

Frohlich, infantile scurvy, 328 

Fructose, 3, 5, 7 

Fruits, 386, 387, 388, 389, 390, 391, 
392, 395 

Fruit sugar, see Fructose 

Fucose, 4 

Fuel requirements, sec Food require- 
ments, Dietary standards, Energy 
metabolism 

Fuel value of food, 138-143, 144, 145, 
147, 407-421 

Fundus, 84 

Funk, acidosis, 315, 328 
deficiency diseases, 328 
isolation of antineuritic substance, 323 

Funk and Schonborn, influence of vita- 
mine-free diet upon carbohydrate 
metabolism, 328 

Furst, experimental scur\'y, 328 

Galactans, 5, 8, 16 

Galactose, 5, 8, 104 

Galactosides, 8, 10 

Garrod, scurvy, 312 

Gastric digestion, 80, 84, 85-89 

Gastric fistula, 70 

Gastric juice, 70, 85-88 

Gaule, absorption of inorganic iron, 290, 

308 
Gautier, dietary standard, 363 
Gelling, nutritive value of diamino acids, 

67 
Gelatin, 48, 52, 55, 57, 61, 142, 225, 

341. 41S 
as supplement to oat diet, 351 
Gephart and DuBois, basal metabolism, 

201 
Gephart and Lusk, analysis and cost of 

ready-to-serve foods, 400 
Gies, classifications of the lipins, 36, 40 
Gillett, food requirements of children, 

400 
Givens and Mendel, calcium and mag- 
nesium metabolism, 283 
Gliadin, 47, 48, 49, 50, 52, 56, 58, 61, 

63, 68, 142, 224, 225, 240, 339, 

342 
Globulins, 52, 54-56, 60, 224, 404 



Glucose, 3, 5, 6-7, 75, 104-110, 117, 

118, 124-126, 142, 216 
Glucosides, 4 

Glutamic acid, 44, 47, 60, 6i, 120, 126 
Glutaminic acid, sec Glutamic acid 
Glutelins, 52, 56, 6i, 404 
Gluten, 56 
Glutenin, 52, 61, 225 
Gluten feed, 423 
Glyceric aldehyde, 105-109, 115, 117, 

125, 216 
Glycerides, 19, 20, 24-27, 332; sec also 

Fats 
Glycerin, see Glycerol 
Glycerol, 19, 107, 115, 117, 216 
Glycerophosphate, 322 
Glycerose, 4 
Glyceryl radicle, 19 
Glycine, 42, 45, 47, 48, 60, 61, 62, 119, 

120, 126, 403 
Glycinin, 60, 225 
Glycocoll, see Glycine 
Glycogen, 5, 14-15, 104, 109, in, 123, 

137, 142, 204, 205 
Glycolaldehyde, 3, 4 
Glycolipins, 36 
Glycolose, 3, 4 
Glycoproteins, 53, 405 
Glycosuria, 6, 124 
Glycyl glycine, 45 
Glyoxals, 124, 125 
Goetsch, influence of pituitarj' feeding, 

355 
Goodall and Joslin, chloride excretion, 

238 
Goose, 423, 429 
Gooseberries, 423 
Gossypol, 353 
Gottlieb, intestinal elimination of iron, 

288, 308 
Grain products, 386, 387, 388, 389, 390, 

391. 392, 394. 397 
Grapes, 395, 415, 423, 429 
Grape butter, 415 
Grapefruit, 395, 415, 423, 429 
Grape sugar, see Glucose 
Growth, 56-68, 193-198, 224-226, 229- 

231, 247-249, 266-267, 300-301, 

310, 331-359 
Griitzner, muscular activity of stomach, 

83,84 



442 



INDEX 



Guanine, 130, 131, 132 

Cluanosine, 132 

Guanylic acid, 132 

Gulosc, 5 

Gumpcrt, metabolism of phosphorus, 

etc., 250, 258 
Gums, 5 
Guava, 423 



Haddock, 415, 423, 429 

HaHbut, 61, 415, 423, 429 

Ham, 145, 415, 423, 429 

Hammarsten's rennin, 78 

Harden and Zilva, a-hydroxypyridine 
and adenine, 328 

Hart, nutritive values of milk and grain 
proteins, 66, 67 

Hart, Halpin, and McCoUum, behavior 
of chickens fed rations restricted 
to cereal grains, 355 

Hart and Humphrey, protein require- 
ments of milch cows, 226 

Hart and McCollum, effects of restricted 
rations, 328, 344, 355, 356 

Hart, McCollum and Fuller, phosphorus 
in nutrition of animals, 248, 258, 
344. 355 

Hart, McCollum and Humphrey, ash 
constituents of wheat bran in 
metabolism of herbivora, 258 

Hart and Steenbock, effect of magne- 
sium upon calcium metabolism. 
270, 2S3 

Hartley, fat of organs, 3C3-31, 40 

Hasselbach, influence of food upon car- 
bon dioxide tension of expired 
air, 281 

Hausermann, inorganic iron in place 
of food iron, 291, 292, 293 

Hawk, water in nutrition, 258 

Hazelnuts, 423, 429 

Heat of combustion, 139-143 

Heat production in body, sec Metab- 
oUsm 

Hematin, 59 

Hematogen, 287 

Hemicellulose, 16 

Hemoglobin, 53, 59, 85, 285, 297, 40S 

Henderson, acid excretion, 273-279, 283 
acidosis, 283 



Henderson — Continued 

carbonic acid and neutrahty, 275, 

276 
equilibrium in solutions of phosphates, 

283 
fitness of the environment, 283 
regulation of neutrality in animal 
body, 273-279, 283 
Henriques and Andersen, nutrition 
through intravenous injection, 
120, 137 
Henriques and Hansen, influence of 
food fat and other conditions 
on body fat of swine, 29, 40 
Heptoses, 5 
Herbst, calcium and phosphorus in 

growth, 258, 266, 267 
Herring, 415, 423, 429 
Herter, bacteria of the digestive tract, 
96-98 103 
calcium metabolism, 263, 266 
Hertz, absorption in large intestine, 93 
Hess, infantile scurvy, 317, 318 
Hess and Fish, infantile scurfy, 317, 

329 
Heterocyclic amino acids, 44 
Hexobioses, 5 
Hexosans, 5 
Hexoses, 5, 132 

Hill, estimation of relative heights and 
weights, 367 
glj'cogen formation during sleep, 117, 
. 118 
Hindhede, dissolving of uric acid as 
affected by food, 281 
proteins and nutrition, 223, 232, 401 
Histidine, 44, 45, 47, 60, 61, 72, 120 
Histones, 52, 404 
Hogan, corn as source of protein and ash, 

356 
Hoist and Frohlich, antiscorbutic prop- 
erty' of food, 313, 329 
Hominy, 394, 415, 423, 429 
Honey, 416, 424, 430 
Hoobler, human milk production, 232 
milk as food protein, 226 
protein need of infants, 232 
Hopkins, accessory factors in normal 
dietaries, 356 
milk as growth-promoting food, 356 
Hordcin, 52, 61 



INDEX 



443 



Hormone, 88, 8g, 276, 34s 

Romberg, checking of secretion of 

gastric juice, 88 
Horseradish, 424 
Howell, arrangement of food in stomach, 

8S 
physiology, 103 

relation of amino acids to metabolism, 
t- 119 
Huckleberries, 416, 424, 430 
Hudek and Stigler, hunger, 82 
Hull and Keeton, gastric lipase, 103 
Human body, elementary composition, 

234 
Hundred-Calorie portions, 144-146, 410- 

420 
Hunger, 81-82 

Hunt, acetonitrile poisoning, 350 
Hutchison, food and dietetics, 401 

normal amomit of protein in diet, 376 
Hydrogen, 234 
Hydrogenation of fats, 23 
Hydrogen ion concentration, influence 

on enzyme activity, 76, 77 
Hydrogen peroxide, decomposition of, 

78 
Hydrolysis, 6, 130 
Hydrolytic cleavage, 130 
Hypogteic acid, 23 
Hypoxanthinc, 130, 132, 133 

Ileocaecal valve, 92, 93, 94 

Ileum, 93, 94 

Indican, 98 

Indol, 98 

Infants, see Children 

Inorganic elements, 234-309, 342-345, 

347-352, 355-359, 3S2-383, 391- 

401, 421-431 
distribution in body, 234, 260 
in American dietaries, 271 
relation to each other, 269, 270 
requirements (quantitative), 252-255, 

262-268, 297-300, 382-383 
Inorganic foodstuffs, 234, 309: see also 

Inorganic elements 
Inositol, 244 

Intestinal digestion, 89-94 
Intestinal juice, 91, 92 
Inulin, 5, 17 
Inversion oi sugar, 9 



Invertase, 77, 103 ; sec also Sucrase 

Invert sugar, 9 

Iodine, 234, 345, 350 

Iodine number of fats, 23 

Irish moss, 17 

Iron, 234, 271, 383 

assim.ilation of, 287, 288 

function in nutrition, 285, 286 

in dietaries, 303, 308, 382-383, 409 

in eggs, 304 

in food, 285, 303, 308, 421-431 

in food materials, tables, 302, 421- 

431 
in grain products, 305, 306 
in meat, 303 

in milk, 300, 301, 304, 305 
in modified milk, 304, 305 
metabolism, 285-301, 306-309 
nutritive relations of, 297, 298 
per cent in body, 285 
requirement, 297-300, 382-383 
reserve supply at birth, 300 
utilization of different forms, 287- 

297, 306, 308-309 
value of inorganic, 286, 296, 297 
vegetables and fruits as sources of, 
306, 307 

Isomaltose, 5 

Isomerization, 326 

Jackson et al., experimental scurN^', 
31S, 316, 329 

Jam, 424 

Janney, metabolic relationship of pro- 
teins to glucose, 137 

Jelly, 424 

Jones, nucleic acids, 131, 134, 137 

Jones and Read, yeast nucleic acid, 137 

Jordan, Hart, and Patten, metabolism 
and physiological effects of phos- 
phorus of wheat bran, 258 

Jordan and Jenter, formation of milk 
fat from carbohydrate, 28, 40 

Kafirin, 52 

Kastle, alkali in ash of human and cow's 
milk, 283 

Katzenstein, oxygen consumption dur- 
ing muscular work, 181, 182 

Kaufi^mann, metabohsm experiment with 
gelatin and amino acids, 55 



444 



INDEX 



Kayser, protein-sparing by fat or car- 
bohydrates, 211, 212 
Keller, slorage of phosphorus, 247 
Kellogg and Taylor, the food problem, 

401 
Kendall, bacteria of digestive tract, 95 
Kephalins, 243 
Ketoses, 3, 4, 5 
Ketoxylose, 4 
Knoop, formation of amino acids from 

ammonium salts. 125 
Knoop and Embdcn, /3-oxidati()n theon,', 

116 
Knoop and Kertcs, a-amino acids and 

a-ketonic acids in the liver, 137 
Kohlrabi, 416, 424, 430 
Koumiss, 416 

Krcis and Hafncr, mixed glycerides, 26 
Krogh, respiratory exchange of animals 

and man, 201 
Kiihnc, introduction of word "enzyme," 

74 
Kulz, carbohydrate formation from 

protein, 124 
Kunkcl and Egers, regeneration of blood 

with medicinal iron, 291 
KjTins, 406 

Lactalbumin, 49, 52, 56, 60, 65, 66, 68, 

225, 226, 339. 340 
Lactase, occurrence and action, 79 
Lactic acid, 75, 105-109, 113, 124, 125, 

126, 216 
Lactose, 5, 10 
Lamb, 416, 424, 430 
Landergren, nitrogen metabolism, 215 
Langworthy, food and diet in United 

States, 401 
results of dietarj' studies, 364, 365, 401 
Langworthy and Milner, respiration 

calorimeter, 169 
Lard, 394, 416 
Laurie acid, 22, 116 
Lawes and Gilbert, formation of fat 

from carbohydrate, 28 
Leathes, synthesis of butyric acid from 

lactic acid, 113 
Lecithans, 243 
Lecithins, 38-39, 243, 322, 323 

in human and cow's milk, 248 
Lecithoproteins, 53, 243, 405 



Leeks, 424 

Legumelin, 52, 60 

Legumin, 49, 52, 56, 60, 142, 240 

I^eipziger, phosphoproteins, 246 

Lemons, 395, 416, 424, 430 

juice, 416, 424, 430 
Lentils, 395, 424, 430 
Lettuce, 146, 395, 416, 424, 430 
Leucine, 43, 47, 60, 61, 72, 78, 120, 126 
Leucosin, 49, 52, 60, 240 
Levene and Meyer, carbohydrate metab- 
olism, 137 
Levin, intestinal bacteria, 95, 96 
Levulans, 5, 17 
I^evulose, see Fructose 
Liebig, high protein diet, 374, 375 
Limes, 424 
Linoleic acid, 24 
Linolenic acid, 24 
Linseed meal, 424, 428 
Lipases, 73, 74, 76, 79, 103 
Lipins, classification of, 36 
Lipoids, 21, 34-41 
Lipolytic enzymes, sec Lipases 
Litten, scurvy, 329 
Little, beriberi caused by fine white 

flour, 329 
Liver, 416 
Lloyd's reagent, 325 
Ijobster, 416 
Lowy and Zuntz, influence of war diet 

on metabolism, 201 
Lupeose, 5 
Lupins, 424, 428 

Lusk, calcium rich diet during preg- 
nancy, 265 

chemical regulation of temperature, 
192 

energy requirements, 180, 187 

food economics, 401 

food values, 401 

formation of carbohydrate from pro- 
tein, 124 

hydrolysis of nucleotides, 132 

i-nfluence of food on metabolism, 190, 
201 

nutrition, 117, 137, 169, 201, 232, 
283, 329, 356, 401 

protein metabolism, 211 
and muscular activity, 229 

regulation of metabolism, 178 



INDEX 



445 



Lusk — Continued 

specific dynamic action, igo, 201 
yield of carbohydrate from protein, 
127 
Lusli, Rich, and Sodcrstrom, respiration 

calorimeter, 169 
Lyman, metabolism of fats, 137 
Lymphatic radicles, 90 
Lysine, 44, 47, 48, 60, 61, 62, 63, 72, 120, 

216, 224, 226, 339, 341, 342 
Lyxose, 4 

Macallum, absorption of iron, 290, 309 
MacLean and Williams, fat of tissues 
and organs, 40 

phospholipins in liver fat, 39 
jMcClendon, formation of fat from pro- 
tein, 40 
McCollum, causes of failure of food to 
nourish, 347, 348 

deficiencies of individual foods, 334, 
335, 347, 352, 356 

dietary relationships among foods, 329, 
356 

effect of acid-forming food, 281 

fat-soluble A in plant tissue, 333 

growth and development, 334, 346 

growth promoting property of butter 
fat, 346 

rfuclein synthesis, 258 

nutritive values of milk and grain pro- 
tein, 66, 67, 226, 232, 356 

repair processes in protein metabolism, 
232 

value of inorganic phosphates, 248, 249 
McCollum and Davis, essential factors 
in diet during growth, 356 

growth promoting influence of butter 
fat, 39, 332, 356 

influence of certain vegetable fats on 
growth, 356 

influence of mineral content of ration 
on growth, 356 

influence of plane of protein intake on 
growth, 232, 356 

nature of dietary deficiencies of rice, 
356 

nutrition with purified food sub- 
stances, 356 
McCollum, Halpin, and Drescher, syn- 
thesis of lecithin, 249, 258 



McCollum and Hoagland, endogenous 
nitrogen metabolism, 283 

McCollum and Kennedy, dietary fac- 
tors in production of polyneuritis, 
329, 347 

McCollum and Pitz, vitamine hypothesis 
and deficiency diseases, 329 

McCollum and Simmonds, biological 
analysis of pellagra-producing 
diets, 356 

McCollum, Simmonds, and Pitz, dietary 
deficiencies of the maize kernel, 
357 

of oat kernel, 357 
of wheat embryo, 356 
of white bean, 357 
distribution in plants of fat soluble 

A, 357 
effects of feeding proteins of wheat 
kernel at difi'erent planes of in- 
take, 232, 357 
effect upon growth of adding salt 

mixture to ration, 34s 
is lysine the limiting amino acid in 
proteins of wheat, maize, or oat 
kernel?, 357 
relation of unidentified dietary fac- 
tors to growth-promoting prop- 
erties of milk, 357 
vegetarian diet in light of present 
knowledge of nutrition, 357 

McCrudden, nutrition and growth of 
bone, 357 

McCrudden and Fales, mineral metabo- 
lism in intestinal infantilism, 258 

McKay, protein element in nutrition, 
232, 401 

Maize, 350, 351 

Maize glutelin, 61, 225 

Macaroni, 394, 416, 424 

Mackerel, 416, 424, 428 

Magnesium, 234, 271, 272 

Magnus-Le\-y, respiratory quotient and 
metabolism, iii, 154, 155 

Maltase, 79 

Malt amylase, 77 

Malt sugar, see Maltose 

Maltose, 5, 10, 11, 86 

Manganese, 234 

Mango, 424 

Mangolds, 424 



446 



INDEX 



Mannans, s, i6 

Mannohcptose, s 

Mannose, s 

Manny, average weights and rates of 

growth of children, table, 372 
Manometer, 81 
Maple syrup, 424, 430 
Marcuse, value of phosphoproteins, 246 
Marmalade, 416 

Marshall, comparative value of organic 
and inorganic phosphorus, 2^2, 
258 
Masslow, metabolism of organic phos- 
phorus, 250 
phosphorus for growing organism, 259 
Mastication, iqi 

Mathews, fats and lipoids in the body, 35 
influence of mental activity on metab- 
olism, 177 
lipins, 36, 40 

physiological chemistry, 103, 137, i6g, 
202, 283 
Means, basal metabolism and body sur- 
face, 174, 202 
Means, Aub, and DuBois, effect of 
caffeine on heat production, 202 
Meat, 386, 387, 388, 389, 390, 391, 392, 

394. 397, 398, 424. 430 
Mechanical efficiency of man, 181-185, 

200 
Meeh's formula for computing body 

surface, 172 
Meischer, formation of organic phos- 
phorus compounds, 246, 259 
Melezitose, 5 
MeHbiose, 5 

Meltzer, advantage of high protein diet, 
378, 379 
calcium, importance of, in the body, 

270 
factors of safety in animal structure 
and economy, 401 
Mendel, abnormalities of growth, 357 
changes in food supply and relation 

to nutrition, 401 
gain in body weight of children, 230 
nutrition and growth, 67, 233, 357 
viewpoints in study of growth, 357 
sec also Osborne and Mendel 
Mendel and Daniels, behavior of stained 
fats in body, 40 



Mendel and Judson, changes in water, 
fat, and ash content of body dur- 
ing growth, 338, 339 
influence of dilTerent types of stunting 

upon body composition, 342 
relations between diet, growth, and 
composition of the body, 357 
Mendel and Osborne, growth, 357 ; see 

also Osborne and Mendel 
Metabolism, at various ages, 193-198 
basal, 151-168, 170-179 
behavior of foodstuffs in, 104-137, 

138 
conditions affecting, 170-233 
definition of, xi 
during fasting, 188, 189, 200 
effect of muscular work, 179, 180 
energy requirement in, 148-202 
fate of foodstuffs in, 104-137 
in disease, 178 

influence of age and growth, 193-198 
food, 188-191, 201, 202, 207-217 
muscular work, 179-188, 226-229 
previously stored fat and glycogen, 

204-207 
size, etc., 170, 171, 174, 175 
temperature, 191-193 
thyroid, 178 
internal activities, and secretions, 175, 

178 
mineral, 234-309 

calcium, 260-268, 272, 282-284 
iron, 285-309 
phosphorus, 242-259 
sulphur, 239-242 
protein, 1 18-137, 203-233, 374-382 
of adults, 170-202 
of growing children, 196, 197 
purine, 130-134, 136-137 
Metaproteins, 53, 405 
Methyl glyoxal, 105, 106, 107, 108, 109, 

115, 126, 216 
Methylpentoses, 4 
Metschnikoff, intestinal bacteria, 96 
Metschnikoff and Woolman, intestinal 

putrefaction, 103 
Michaelis, hydrogen ion concentration, 

283 
Milk, 146, 241. 256, 269, 289, 302, 353, 
386, 387, 388, 389, 390, 391. 392, 
394. 397> 398, 416, 424, 430 



INDEX 



447 



Milk sugar, see Lactose 

Millet, 42s 

Millon reaction, 71 

MiUs, injection of fatty oils, 117 

Mince meat, 417 

Mineral elements, see Ash constituents, 
also Inorganic elements 
function of, 236 

Mineral metabolism, 234-3og 

Mitchell, feeding isolated amino acids, 67 

Molasses, 3S6, 387, 388, 389, 390, 391, 
392, 417, 425, 430 

Molecular weights of proteins. 50 

Monaminodicarboxylic acids, 44 

Monaminomonocarboxylic acids, 43 

Monosaccharides, 2, 4, 5, 6, 8, 17-18, 
79, 104 

Monosaccharoses, 4, 6-8, 17-18, 79, 104 

Moore and Bergin, reaction of intestinal 
contents, 92 

Morgulis, influence of feeding on metab- 
oHsm, 202 

Moro, intestinal bacteria, 96 

Moulton and Trowbridge, composition 
of beef fat, 30, 40-41 

Mucilages, 5 

Mucins, 53 

Mulder, on protein, 42 

Mujik, storage of food fat in the body, 32 

Murlin, energy requirement in preg- 
nancy, 199 
nutritive value of gelatin, 233 
respiration incubator for study of 
energy metabolism, 202 

Murlin and Bailey, energy requirement 
of new-born, 195 
protein metabolism in pregnancy, 233 

Murlin and Greer, heart action and 
energj' requirement, 175 

Murlin and Hoobler, metabolism of chil- 
dren, 202 

Murlin and Lusk, influence of ingestion 
of fat, 202 

Muscular work, 179-188, 226-229 

Mushrooms, 417, 425 

Muskmelons, 417, 425, 430 

Mustard, 425 

Mutases, 76 

Mutton, 417, 425, 430 

Myosin, 49, 52, 240, 247 

Myristic acid, 22, 116 



Nectarines, 417 ^ 

Nef, behavior of sugars, 7, 17 
Nencki, formation of fatty acids, 114 
Nelson, phosphorus content of starch, 

13, 18 
Nelson and Vosburgh, kinetics of in- 

vertase action, 103 
Nelson and WilUams, calcium output, 

264, 283 
Neumann, dietary study, 150, 151 
Neutrality, 77, 273-284 
Nicotinic acid, 327 
Nitrogen, balance experiments, 207, 208, 

209, 210, 215 
distribution of excreted, 135, 136 
fate in protein metaboUsm, 128 
in body, 234 
metabolism, 130 
see also Protein 
Northrup, phosphorus content of starch, 

13, 18 
Northrup and Nelson, phosphorus in 

starch, 244 
Nothnagel, practical medicine, 309 
Nucleic acids, 130-137 
Nuclein, 131 

Nucleoalbumins, see Phosphoproteins 
Nucleoproteins, 53, 130, 131, 243, 405 
Nucleosides, 131, 132 
Nucleotidases, 131, 132 
Nucleotides, 132; see also Nucleic acid 
Nutritive ratio, 147, 148 
Nutritive requirements, see Energj-, 

Food, and under the individual 

nutrients 
Nuts, 3S6, 387, 388, 389, 390, 391, 392, 

395 
Nuttall and Thierfelder, intestinal bac- 
teria, 95 

Oatmeal, 146, 241, 256, 269, 302, 394, 

417, 42s, 430 
Octoic acid, 113, 114 
(Edema, 324 

Ohler, experimental polyneuritis, 329 
Okra, 417, 425 
Oleic acid, 23 
Olein, 23, 30 

Olives, 395, 417, 425, 430 
Olive oil, 146, 394 
Onions, 395, 417, 425, 430 



448 



INDEX 



Oppenhcimcr, enzymes, 103 

Oranges, 146, 256, 269, 302, 395, 417, 

42s. 430 
Ornithine, 44, 129 
Orj'z^nine. 324, 325 
Osborne, chemical nature of diastase, 

72, 73 

ratio of nitrogen to sulphur, 240 

plant proteins, 60, 61, 68 

structure of proteins, 47, 49 

sulphur in proteins, 283 
Osborne and Mendel, acceleration of 
growth after retardation, 358 

amino acids in nutrition and growth, 
358 

bacteria in feces, 103 

cottonseed flour, 354 

efBciency of individual proteins, 233 

experiments with isolated food sub- 
stances, ss-68, 224, 357 

experiments with restricted amounts 
of adequate proteins, 340 

gliadin in nutrition, 358 

growth upon diets of isolated food 
substances, 358 

growth-promoting effect of protein- 
free milk, 332 

influence of butter fat and other fats 
on growth, 39, 358 

nutritive factors in animal tissues, 358 

nutritive properties of proteins, 55- 
68, 224-226, 233, 339-342, 358 

problem of protein minimum, 358 

relation of growth to chemical con- 
stituents of diet, 55-68, 224-226, 
233, 339-346, 358 

relative efficiency of proteins, 55-68, 
225, 226, 358 

resumption of growth after long con- 
tinued failure to grow, 358 

soy bean as food, 358 

stability of growth-promoting sub- 
stance of butter fat, 358 

suppression of growth, 57, 63, 64, 224, 

341 

vitamines, role of, in diet, 329 

zein in growth, 66, 224, 340 
Osborne, Mendel, and Ferry, effect of 
retardation of growth upon breed- 
ing period and duration of life, 
35S 



Osborne, Van Slyke el al., products of 

hydrolysis of proteins, 68 
Ovalbumin, 225 

Ovovitellin, 49, 53, 61, 225, 243, 246 
Oxidases, 75 
Oxygen, 234 

consumption, 181 
Oxyhemoglobin, 49, 50, 53 
Oxyproline, 61 
Oxypurine, 132 
Oysters, 417, 425, 430 

Palmitic acid, 22, 116 

Pancreatic juice, 90, 91 

Paprika, 425 

Parsnips, 395, 417, 425, 430 

Passage of different foods through the 
digestive tract, 86, 87, 89, 92, 
93 

Paton, formation of complex phosphorus 
compounds, 246 

Pawlow, digestion, 80, 87, 103 

Peaches, 146, 395, 417, 425, 430 

Peanuts, 146, 256, 269, 302, 395, 418, 
425, 430 

Pearl, effect of feeding pituitary sub- 
stance and corpus luteum on 
egg production and growth, 359 

Pears, 395, 418, 425, 430 

Peas, 241, 302, 395, 418, 425, 430 

Pea soup, 417 

Pecans, 395, 425, 430 

Pectins, 5, 17, 18 

Pekelharing, pepsin, 71, 72 

Pentosans, 5, 11 

Pentoses, 4, 132 

Peppers, 418, 425, 430 

Pepsin, 71, 73, 77, 80 

Peptids, 45, 54, 406 

Peptones, 54, 59, 73, 406 

Perch, 430 

Peristalsis, 85, 90-94 

Persimmons, 418, 425, 430 

Petit, pepsin, 78 

Pfliiger, fat formation, 127 
glycogen, 137 

Phaseolin, 52, 60 

Phenol, 98 

Phenylalanine, 43, 45. 47, 60, 61, 125, 
126, 403 

Phlorizin diabetes, 118, 124 



INDEX 



449 



Phosphates, 243-259, 276-283 ; sec also 

Phosphorus 
Phosphatids, 37, 38-39, 243, 244, 246, 

322 ; sec also Phospholipins 
Phospholipins, 36, 38-39, 243, 244, 246, 

322 
Phosphoproteins, 243, 244, 246, 405 
Phosphoric add, 39, 131, 132, 243-24S, 

276-283 
Phosphorus, 234, 271, 272, 383 
amounts in dietaries, 255, 256, 257, 

391-396 
amounts in food materials, 256 
comparative value of organic and 

inorganic, 250, 252 
compounds, classified, 243 
effect of deficiency, 343, 344 
excretion, 253 

metabolism, 242, 244, 254, 255 
requirement, 252, 253, 255, 383, 391- 

396 
Photosynthesis, i, 2 
Phycetoleic acid, 23 
Phytates, 244, 246 
Phytic acid, 244 
Phytin, 322, 323 
Phytosterol, 37 
Phytosynthesis, i, 2 
Pies, 418 
Pignolias, 418 

Pineapple, 146, 395, 418, 425, 430 
Pine nuts, 418 
Pistachios, 418 
Pitcairn, triturating action of stomach, 

70 
Playfair, dietary standard, 363 
Plimmer, constitution of proteins, 68 
metabolism of organic phosphorus 

compounds, 259 
Plums, 146, 395, 418, 42s, 430 
Polyneuritis. 318, 321, 327 
Polypeptids, 46, 54, 403 
Polysaccharides, 4, 5, 11-18 
Polysaccharoses, 4, 5, 11-18 
Pomegranates, 418, 426 
Pork, 418, 426, 430 
Portions, Standard or loo-Calorie, of 

foods, 144-146, 410-420 
Potassium, 234, 237, 271, 272 
Potatoes, 146, 241, 256, 269, 302, 395, 

418, 426, 430 

2 G 



Pottcvin, reversion of enzyme action, 79 
Poullr>', 386, 387, 388, 389, 390. 391. 392 
Prausnitz, composition of feces from 

different diets, 99 
Primary protein derivative, 53, 405, 406 
Prohne, 44, 47, 56, 60, 61, 126 
Protamins, 53, 404 
Proteans, 53, 405 
Proteases, 74, 75 
Proteid, 403 
Protcin(s), 42-68, 403 
absorption of, 119 
acid-, 54 

alcohol-soluble, 404 
alkali-, 54 

allowance, 376-380, 381 
classification, 51-54, 403-406 
coagulated, 54, 406 
complete, 224, 225 
composition of, 4S-50 
conjugated, 53, 405 
derivatives, 53, 54, 405-406 
derived, 53, 405 
energy value of, 142, 143 
general properties, 42-51 
hydrolysis of, 46, 47, 118 
incomplete, 225, 340, 341 
injection of, 1 20 

in growth, 55-68, 339-34°. 355-358 
in neutraUty, 278 
metabolism, 1 18-137, 203-233, 339- 

342, 373-382 
in fasting, 203, 204 
influence of body fat, 205, 206 
molecular weights, 50 
opinions upon Uberal diet, 374, 375, 

376, 377 
partially incomplete, 225 
primarj' derivatives, 53, 405 
properties, of individual, 54-67 

physical, 51 
putrefaction of, 97 

requirement, 217-220, 339-340, 373- 
382, 383 
determining factors, 203 
effect of muscular exercise, 227 
influence of choice of food, 222, 223 
relation to age and growth, 229, 

230, 231 
results of experiments, 220 
versus protein standard, 220-222 



450 



INDEX 



Protcin(s) — Continued 

respirator>' quotient, no, in 

secondarj' derivatives, 406 

simple, 52, 403, 404 

sparing, 210-217 

standard, 220-222, 273, 274, 373- 
382, 383 
for children, 381, 382-383 
for families, 382-383 

utilization in tissues, 122, 123 

value of high intake, 375, 378, 379 
Proteolytic enzyme, see Proteases 
Proteoses, 54, 59, 73, 406 
Prunes, 146, 256, 269, 302, 395, 419, 

426, 430 
Psychic factors in digestion, 80-83, 88 
Ptyalin, 73, 76, 79, 83, 86 
Pumpkins, 419, 426, 430 
Purines, 130, 131, 327 
Putrefaction, 98 
Putrefactive bacteria, 97, 98 
Pylorus, 83, 84, 8s, 86 
Pyridines, 326, 327 
Pyrimidines, 131, 133, 323, 327 
Pyruvic acid, 108, 109, 114, 125, 216 
Pyruvic aldehyde, 124, 125; see also 
Methyl glyoxal 

Radishes, 395, 419, 426, 430 

Raffinose, s 

Raisins, 146, 395, 419, 426, 430 

Raper, normal octoic acid, 114 

Raspberries, 419, 426, 430 

Rate of passage of foods through the 

digestive tract, 86, 87, 89, 92, 93 
Reaumur, gastric digestion, 70 
Reductases, 75 
Regulation of body temperature, 191- 

193 
Reichert, differentiation and specificity 

of starches, 12, 18 
Relation of height and weight, 367-370, 

372, 373 
Rcnnin, 75, 78 
Requirements, see Food Requirements; 

see also Metabolism ; also Stand- 
ard 
Resorption, 93 
Respiration experiments, 151; see also 

Calorimeter 
work of, 168 



Respiratory quotient, 109, no. ni, 

152. 153. 154. 187 
Rettger, influence of milk feeding on 

mortality and growth, 359 
Ribose, 4, 132 

Rice, 146, 256, 269, 302, 350, 394, 419, 
426, 430 
protein, products of hydrolysis, ref.. 68 
Richardson (A. E.), and Green, cotton- 
seed flour, 353, 359 
Richardson (W. D.), chemical character- 
istics of lard, 41 
Riche, adiabatic bomb calorimeter, 140 
Rhamnose, 4 
Rhubarb, 419, 426, 430 
Robertson, chemical mechanism main- 
taining neutrality, 283 
growth, and growth-controlling sub- 
stances of pituitary body, 359 
Roentgen rays, 84, 86, 92, 93 
Rohmann, phosphoproteins versus in- 
organic phosphates, 247 
Romaine (salad), 426 
Rona, absorption of amino acids, 1 20 
Rose, creatinuria, 137 
Rose and Cooper, potato nitrogen, 224, 

233 
Rubner, fenergy metabolism, 169, 170 
fuel values of food constituents, 143 
influence of food on metabolism, 189, 

190 
relation of body surface to metabo- 
lism, 171 
specific dynamic action of foodstuffs, 
189-190 
Rubner and Heubner, storage of food 

for growth, 194 
Rutabagas, 426, 430 
Rye, 426, 430 

Saccharose, see Sucrose 
Salivary digestion, 80, 82-84 
Salmon, 146, 419, 426, 430 
Salt, craving for, 237-239 

effect upon metabolism, 239 
Saponification, 19 
Sapota, 426 
Sausage, 419 
Scallop, 61 

Schaumann, beriberi, 322, 329 
Schlossmann, phosphorus in milk, 259 



INDEX 



451 



Schondorfl, distribution of glycogen in 

the body, 15 
Schmidt, medicinal iron in hemoglobin 

formation, 296 
Schmidt and Strassburger, composition 

of feces; ref. 103 
Schottelius, bacterial action in digestion, 

95. 96 

Schryver and Haynes, pectins, 18 

Schulze and Reineke, composition of 
fat of different mammals, 30 

Schwann, pepsin, 71 

Score value, 392-395 

Scurvy, 310-318, 327-329 

Secalose, 5 

Secondary protein derivatives, 54 

Secretin, 91, 92 

Sedoheptose, s 

Seeds, deficiency as sole food, 352, 353 

Seegen, formation of carbohydrate from 
protein, 123 

Seidell, antineuritic vitamine, 325, 329 

Serine, 43, 45. 47, 60, 61, 126 

Serum globulin, 49, 52, 240 

Sex, relation to food requirement, 199, 
264-265, 300, 371, 372 

Shad, 419 

Shaffer, nitrogen output during rest and 
work, 229 

Sherman, iron in food and nutrition, 
298-309 

Sherman and Baker, starch, 13, 18 

Sherman and Gettler, balance of acid- 
forming and base-forming ele- 
ments, 279-280, 283 
chemical nature of enzyme prepara- 
tions, 103 

Sherman and Gillett, adequacy and 
economy of city dietaries, 401 

Sherman, Mcttler and Sinclair, calcium, 
magnesium, and phosphorus in 
food and nutrition, 259 

Sherman and Schlesingcr, pancreatic 
amylase preparation, 78, 103 

Shredded wheat, 419, 426, 430 

Shrimp, 426 

Silicon, 234 

Sitosterol, 37 

Siven, protein requirement, 233 

Size, relation to metabolism, 170-175; 
see also Age; Children 



Sjostrom, influence of temperature on 
carbon dioxide output, 202 

Skatol, 98 

Skraup and Behler, structure of gela- 
tin, 47 

Smedley, formation of fat from carbo- 
hydrate, 41, 114, 115 

Snell, bomb calorimeter, 139 

Socin, experiments with organic and 
inorganic iron, 288, 309 

Soderstrom, Meyer, and DuBois, com- 
parison of metabolism of men 
flat in bed and sitting in steamer 
chair, 202 

Sodium, 234, 271, 272 

Soluble starch, 14 

Sonden and Tigerstedt, energy metabo- 
lism, 157 

Sorbose, 5 

Sorensen, hydrogen ion concentration, 
■ 77 

Soup, 426 

Spallanzani, gastric juice, 70, 71 

Specific dynamic action of foodstuffs, 
189-191, 201, 202 

Spinach, 146, 302, 395, 419, 426, 430 

Squash, 395, 419, 426, 430 

Stachyase, 5 

Standards, dietary, 361-367, 382, 383, 
385 
for calcium, 267, 382, 383 
for energy, 183, 186, 187, 196-197, 

360-373 
for iron, 299-300, 382, 383 
for phosphorus, 255, 382, 383 
for protein, 220-222, 229-233, 373- 
383. 385 

Starch, 5, 12-14, i7. 18, 73, 83, 142 

Starch sugar, see Glucose 

Starling, hormones, 88, 89 
physiology of digestion, 103 
secretion of bile, 91 

Steapsin, 90 

Stearic acid, 22, 116, 216 

Stearin, 216 

Steenbock and Hart, calcium require- 
ment of animals, 265, 284 

Steenbock, Nelson, and Hart, acidosis, 
284 

Steinitz, phosphoproteins, 246 

Stepp, lipoids, 39-40 



452 



INDEX 



Sterols, 36, 37-38 

Stevens, experiments with gastric juice, 

70 
Stockman, absorption of inorganic iron, 
289, 290 
iron requirement, 298 
Stoeltzner, significance of calcium in 

growth of bone, 284 
Stoklasa, iron-protein compound of 

onion, 306 
Stomach, 82-89 
Strawberries, 419, 426, 430 
Substrate, 76 

Sued, metaboUsm during fasting, 206 
Succotash, 419 
Succus entericus, 89 
Sucrase, 77, 79, 92, 103 
Sucrose, s, 8-10, 142 
Sugar, 2, 146, 386, 387, 388. 389. 390. 
391, 392, 394, 419; see also Su- 
crose 
double, 4 
references, 17, 18 
simple, 2 
Sulpholipins, 36 
Sulphur, 234-242, 271, 272 
elimination, 242 
metabolism, 239, 240, 241 
proportion in protein, 49, 240, 241 
Suzuki, Shamimura, and Odakc, or>'za- 

nine, 329 
Swartz, utiUzation of cellulose, 16, 18 
galactans, 17, 18 
mannans, 16, 18 
pentosans, 11, 18 
Sylvius, fermentation and digestion, 69 
Symonds, tables of heights and weights, 

368 
Syntonin, 54 

Tagatose, 5 

Takaki, beriberi, 319 

Talbot, energy requirement of infants, 

202 
Tallquist, protein-protecting powers of 

fat and carbohydrate, 212-214 
Talose, 5 
Tamarind, 426 
Tangl, metaboUsm of an artificially fed 

child, 284 
Tapioca, 426, 430 



Tartakowsky, assimilation of inorganic 

iron, 295, 309 
Tashiro, carbon dioxide production in 

nerve, 177, 202 
Taylor, diet of prisoners of war in 
Germany, 401 

digestion and metabolism, 103 

fats and lipoids in body, 35 
Temperature, sec Regulation 
Terminolog>' of hydrolj'tic enzymes, 76 
Tetrahexoses, 5 
Tetranucleotides, 131 
Tetrasaccharides, 5 
Tetrasaccharoses, ', 
Tetroses, 4 

Thioamino acid, see Cystine 
Thomas (A. W.), constitution of starch, 
13. 18 

phosphorus content of starch, 13, 18 
Thomas (K.), nutritive efficiency of 

proteins, 223 
Threose, 4 

Thrombin or thrombase, 75 
Thymine, 131, 132, 133 
Thymonucleic acid, 53 
Thymus, 132 
Thyroid, 178 

Tigerstedt, ash content of ordinary 
dietary, 284 

estimates of food requirements, 186, 
187 

metaboUsm at various ages, 194 

metaboUsm during fasting, i8g 
Tomatoes, 146, 395, 419, 426, 430 
Toruline, 324, 325 
Transportation, effect upon prices, 398, 

390 
Trehalose, 5 

Triglycerides, simple and mixed, 24-27 
Trigonelline, 327 
Trihexoscs, 5 
Triolein, 79 
Trioses, 4 
Trioxypurine, 132 
Tripeptids, 46 
Trisaccharides, 5 
Trisaccharoses, 5 
Triticonucleic acid, 53 
Truffles, 426 
Trypsin, 77, 80, 90, 92 
Trypsinogen, 92 



INDEX 



453 



Tryptophane, 44, 45, 47, 48, 60, 61, 62, 
63, 71- 120, 127, 224, 339, 341 

Tuberin, 52 

Tubular glands, 91 

Tuna, 419 

Turanose, 5 

Turkey, 419 

Turnips, 146, 256, 269, 302, 395, 420, 
426, 430 

Tyrosine, 43, 45, 47, 60, 61, 125 

Underhill, metabolism of ammonium 

salts, 137, 284 
Uracil, 131, 132, 133 
Urea, 129, 142 
Uric acid, 130-134, 281 
Uricolysis, 134 
Uridine, 132 
Uridine nucleotide, 132 
Urine, acidity, 281 

Valine, 43, 47, 48, 60, 61, 120, 126 

Van Slyke, amino acids in intermediary 
metabolism, 1 1 9-1 2 2 
amino acids in physiology and pathol- 
ogy, 137 

Van Slyke et al., fate of protein digestion 
products, 1 19-122, 137 

Van Slyke, Cullen, Stillman, and Fitz, 
acid excretion and alkaline re- 
serve, 284 

Van Slyke and Meyer, absorption and 
distribution of amino acids, 119- 
120 

Von Hehnont, digestion, 69 

Von Hosslin, relation of size to heat 
production, 171 

Von Noorden, metabolism dependent 
upon build of body, 174 
metaboHsmand medicine, 169, 202, 233 
need for high protein intake, 375, 376 
nitrogen equiUbrium, 207-210 
use of vegetables in feeding children, 
308 

Von Wendt, dicalcium phosphate, 247, 
309 
iron requirements, 298, 309 

Veal, 420, 427, 430 

Vedder, beriberi, 330 

Vegetables, 386, 387, 388, 389, 390, 391, 
392, 394. 397, 398 



Vegetable soup, 420 

Venous radicles, 90 

Vernon, intracellular enzymes, 103 

Vicilin, 60 

Vignin, 52, 60 

Vinegar, 427, 430 

Vitamines, xii, 323, 324, 325, 345 

Voegtlin, vitamines, 330 

V'oegtUn and White, can adenine acquire 
antineuritic properties, 330 

Voit, calcium in animal nutrition, 284 
dietary standard, 362 
effects of insufficient calcium, 262 
fat production from protein, 127 
food requirement, 180, 362 
iron metabolism in dogs, 288, 289 
nitrogen elimination in fasting, 204 
phosphorus metabolism during fast- 
ing, 253 

Walnuts, 256, 269, 302, 395, 420, 427, 

430 
Water cress, 427, 430 
Watermelon, 420, 427, 430 
Waters, capacity of animals to grow 

under adverse conditions, 359 
experiments with energy-deficient 

diets, 336, 337 
influence of nutrition on animal form, 

359 
Water soluble B, xiii, S33, 345. 347. 

383, 384, see. also Growth 
Waxes, 36 
Weight, relation to height and age, 197, 

368, 369, 371, 372 
Wells, nucleoproteins, 131 
Wheat, 146, 241, 256, 269, 302, 420, 427, 

430 
embryo, 349, 350 
kernel, 349 
Whey, 427, 430 
White bean, 351, 352 
Whitefish, 420 
W'hortleberries, 427, 430 
Willcock and Hopkins, feeding experi- 
ments with zein and amino acids, 

55 
Williams, chemical nature of vitamines, 
330 
relation of chemical structure to anti- 
neuritic action, 326, 327 



454 



INDEX 



Williams and Salecby, treatment of 

human beriljeri, 330 
vitamine preparation, 325 
Williams and Seidell, vitamine of yeast, 

327 
Wilson, nitrogen metabolism during 

pregnancy, 233 
Wine, 427, 430 

Withers and Carruth, gossypol, 353 
Wolffberg, formation of carbohydrate 

from protein, 123 
Woltering, experiments with inorganic 

iron, 290, 309 
Woodyatt, carbohydrate metabolism, 

137 
Work, influence on metabolism, 179- 

188, 226-229 
Wright, scurvy, 313 

Xanthine, 132, 133 
Xanthoprotein test, 71 
Xylans, 5 



Xyloketose, 4 
Xylose, 4 

Yeast, 75, 132 

Yoshikawa, Yana, and Menals, 
beri, 330 



beri- 



Zadik, phosphoproteins, 246 

Zein, 47, 48, 49, 50, 52, 55, 57, 61, 63, 
65, 66, 224, 225, 240, 339 

Zuntz, metabolism experiment with 
ergometer, 185 
respiration mask, 151 
work, and consumption of oxvgen, 
181 

Zuntz and Morgulis, influence of under- 
nutrition on metabolism, 202 

Zuntz and Schumberg, energy values, 
153 

Zwieback, 420 

Zymase of yeast, 75 

Zymogen, 76 



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TABLE OF CONTENTS 

Part I 

Pood Values and Food Requirements. 

The Composition of Food Materiai-s. 
The Functions of Food. 

Food as a Source of Energy. 

Food as Building Material. 

Food in the Regulation of Body Processes. 
Food Requirement. 

The Energy Requirement of Normal Adults. 

The Energy Requirement of Children. 

The Energy Requirement of the Aged. 

The Protein Requirement. 

The Fat and Carbohydrate Requirement. 

The Ash Requirement. 

Part II 
Problems in Dietary Calculations. 

Studies in Weight, Measure, and Cost of Some Common Food Materials. 

Relation between Percentage Composition and Weight. 

Calulation of the Fuel Value of a Single Food Material. 

Calculation of the Weight of a Standard or loo-Calorie Portion. 

Food Value of a Combination of Food Materials. 

Distribution of Foodstuffs in a Standard Portion of a Sinu;le Food Material. 

Calculation of a Standard Portion of a Combination of Food Materials. 

Analysis of a Recipe. 

Modification of Cow's Milk to a Required Formula. 

Calculation of the Percentage Composition of a Food Mixture. 

The Calculation of a Complete Dietary. 

Scoring of the Dietary. 

Reference Tables. 

Refuse in Food Materials. 

Conversion Tables — Grams to Ounces. 

Conversion Tables — Ounces to Grams. 

Conversion Tables — Pounds to Grams. 

Food Values in Terms of Standard Units of Weight. 

Ash Constituents in Percentages of the Edible Portion, 

Ash Constituents in Standard or loo-Calorie Portions. 

Appendix 
The Equipment of a Dietetics Laboratory. 



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